[原]零基础学习视频解码之解码声音

　　关于视频解码以及使用SDL显示详情见：[原]零基础学习视频解码之解码图像 

　　SDL播放声音的方式是这样的：

　　你建立你的音频选项：采样率（在SDL中称为"频率"），通道数，等等，我们还应该设置一个回调函数和用户数据。当我们开始播放音频，SDL会不断的回调这个函数，让它充满一定数量字节的音频缓冲区，然后我们把这些信息放到SDL_AudioSpec数据结构中，我们接着调用SDL_OpenAudio，这将打开音频设备，还给我们一个AudioSpec结构。

　　freq：采样率

　　format：我们将给SDL什么样的格式

　　channels：音频通道

　　silence：音频缓冲区默认值，通常为0

　　samples：当SDL向我们请求更多的音频缓冲区的大小的时候设置的

　　callback：回调函数

　　userdata：SDL会给我们的回调void指针的用户数据，我们必须让它知道我们的编解码器上下文

　　现在我们开始获取流音频信息，但我们怎么处理这些信息？解决的办法是要创造一种数据结构，我们可以在audio_callback得到音频数据然后保存获取到的数据包！所以我们要做的是创建一个队列的数据包。ffmpeg甚至还带有一个结构来帮助我们做这：AVPacketList，这仅仅是一个链表的数据包，我们还需要自己维护接受到的数据包队列。

　　首先还是配置Eclipse相关依赖库的环境：

　　Project->Properties->C/C++ General->Path and Symbols->Libraries->Add->SDL、avcode、avutil、avformat、swscale

　　一、定义一个数据结构用来保存AVPacketList队列

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　二、初始化这个数据队列：

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　你会注意到，我们有一个互斥体和条件变量。这是因为SDL用一个单独的线程运行音频处理。如果我们不把排好队，我们真的会毁了我们的数据。接下来我们将看到如何在队列的实现。

　　三、添加一个AVPacket到队列中

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　四、从队列中获取一个AVPacket

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　五、解码音频

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　六、处理call_back

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    return EXIT_SUCCESS;
}

　　七、初始化音频相关的变量

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    return EXIT_SUCCESS;
}

　　八、注册初始化与打开视频相关函数

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);
    

    return EXIT_SUCCESS;
}

　　九、找到第一条视频流和音频流

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    return EXIT_SUCCESS;
}

　　十、注册音频相关设置到SDL_AudioSpec中

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    aCodecCtx = pFormatCtx->streams[audioStream]->codec;
    // Set audio settings from codec info
    wanted_spec.freq = aCodecCtx->sample_rate;
    wanted_spec.format = AUDIO_S16SYS;
    wanted_spec.channels = aCodecCtx->channels;
    wanted_spec.silence = 0;
    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
    wanted_spec.callback = audio_callback;
    wanted_spec.userdata = aCodecCtx;

    return EXIT_SUCCESS;
}

　　十一、初始化音频数据队列并打开音频设备

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    aCodecCtx = pFormatCtx->streams[audioStream]->codec;
    // Set audio settings from codec info
    wanted_spec.freq = aCodecCtx->sample_rate;
    wanted_spec.format = AUDIO_S16SYS;
    wanted_spec.channels = aCodecCtx->channels;
    wanted_spec.silence = 0;
    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
    wanted_spec.callback = audio_callback;
    wanted_spec.userdata = aCodecCtx;

    if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {
        fprintf(stderr, "SDL_OpenAudio: %s
", SDL_GetError());
        return -1;
    }
    aCodec = avcodec_find_decoder(aCodecCtx->codec_id);
    if (!aCodec) {
        fprintf(stderr, "Unsupported codec!
");
        return -1;
    }
    avcodec_open2(aCodecCtx, aCodec, NULL);

    // audio_st = pFormatCtx->streams[index]
    packet_queue_init(&audioq);
    SDL_PauseAudio(0);

    return EXIT_SUCCESS;
}

　　十二、初始化与Video相关的环境变量

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    aCodecCtx = pFormatCtx->streams[audioStream]->codec;
    // Set audio settings from codec info
    wanted_spec.freq = aCodecCtx->sample_rate;
    wanted_spec.format = AUDIO_S16SYS;
    wanted_spec.channels = aCodecCtx->channels;
    wanted_spec.silence = 0;
    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
    wanted_spec.callback = audio_callback;
    wanted_spec.userdata = aCodecCtx;

    if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {
        fprintf(stderr, "SDL_OpenAudio: %s
", SDL_GetError());
        return -1;
    }
    aCodec = avcodec_find_decoder(aCodecCtx->codec_id);
    if (!aCodec) {
        fprintf(stderr, "Unsupported codec!
");
        return -1;
    }
    avcodec_open2(aCodecCtx, aCodec, NULL);

    // audio_st = pFormatCtx->streams[index]
    packet_queue_init(&audioq);
    SDL_PauseAudio(0);

    // Get a pointer to the codec context for the video stream
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;

    // Find the decoder for the video stream
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL) {
        fprintf(stderr, "Unsupported codec!
");
        return -1; // Codec not found
    }
    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
        return -1; // Could not open codec

    // Allocate video frame
    pFrame = avcodec_alloc_frame();

    pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
            pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,
            AV_PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);

    return EXIT_SUCCESS;
}

　　十三、初始化视频输出环境

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    aCodecCtx = pFormatCtx->streams[audioStream]->codec;
    // Set audio settings from codec info
    wanted_spec.freq = aCodecCtx->sample_rate;
    wanted_spec.format = AUDIO_S16SYS;
    wanted_spec.channels = aCodecCtx->channels;
    wanted_spec.silence = 0;
    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
    wanted_spec.callback = audio_callback;
    wanted_spec.userdata = aCodecCtx;

    if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {
        fprintf(stderr, "SDL_OpenAudio: %s
", SDL_GetError());
        return -1;
    }
    aCodec = avcodec_find_decoder(aCodecCtx->codec_id);
    if (!aCodec) {
        fprintf(stderr, "Unsupported codec!
");
        return -1;
    }
    avcodec_open2(aCodecCtx, aCodec, NULL);

    // audio_st = pFormatCtx->streams[index]
    packet_queue_init(&audioq);
    SDL_PauseAudio(0);

    // Get a pointer to the codec context for the video stream
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;

    // Find the decoder for the video stream
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL) {
        fprintf(stderr, "Unsupported codec!
");
        return -1; // Codec not found
    }
    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
        return -1; // Could not open codec

    // Allocate video frame
    pFrame = avcodec_alloc_frame();

    pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
            pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,
            AV_PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);

    // Make a screen to put our video

#ifndef __DARWIN__
    screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);
#else
    screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 24, 0);
#endif
    if (!screen) {
        fprintf(stderr, "SDL: could not set video mode - exiting
");
        exit(1);
    }

    // Allocate a place to put our YUV image on that screen
    bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,
    SDL_YV12_OVERLAY, screen);

    return EXIT_SUCCESS;
}

　　十四、循环读包，并根据是音频包还是视频包，做相应处理

/*
 ============================================================================
 Name        : VideoDecodeTutorial2_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"
#include "SDL/SDL_thread.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/pixfmt.h"
#include "libswscale/swscale.h"

#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

typedef struct PacketQueue {
    AVPacketList *first_pkt, *last_pkt;
    int nb_packets;
    int size;
    SDL_mutex *mutex;
    SDL_cond *cond;
} PacketQueue;

PacketQueue audioq;

int quit = 0;

void packet_queue_init(PacketQueue *q) {
    memset(q, 0, sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}

int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (av_dup_packet(pkt) < 0) {
        return -1;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -1;
    pkt1->pkt = *pkt;
    pkt1->next = NULL;

    SDL_LockMutex(q->mutex);

    if (!q->last_pkt)
        q->first_pkt = pkt1;
    else
        q->last_pkt->next = pkt1;
    q->last_pkt = pkt1;
    q->nb_packets++;
    q->size += pkt1->pkt.size;
    SDL_CondSignal(q->cond);

    SDL_UnlockMutex(q->mutex);
    return 0;
}

static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
    AVPacketList *pkt1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {

        if (quit) {
            ret = -1;
            break;
        }

        pkt1 = q->first_pkt;
        if (pkt1) {
            q->first_pkt = pkt1->next;
            if (!q->first_pkt)
                q->last_pkt = NULL;
            q->nb_packets--;
            q->size -= pkt1->pkt.size;
            *pkt = pkt1->pkt;
            av_free(pkt1);
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf,
        int buf_size) {

    static AVPacket pkt;
    static uint8_t *audio_pkt_data = NULL;
    static int audio_pkt_size = 0;
    static AVFrame frame;

    int len1, data_size = 0;

    for (;;) {
        while (audio_pkt_size > 0) {
            int got_frame = 0;
            len1 = avcodec_decode_audio4(aCodecCtx, &frame, &got_frame, &pkt);
            if (len1 < 0) {
                /* if error, skip frame */
                audio_pkt_size = 0;
                break;
            }
            audio_pkt_data += len1;
            audio_pkt_size -= len1;
            if (got_frame) {
                data_size = frame.linesize[0];
                /*
                 data_size = av_samples_get_buffer_size(NULL,
                 aCodecCtx->channels, frame.nb_samples,
                 aCodecCtx->sample_fmt, 1);
                 */
                memcpy(audio_buf, frame.data[0], data_size);
            }
            if (data_size <= 0) {
                /* No data yet, get more frames */
                continue;
            }
            /* We have data, return it and come back for more later */
            return data_size;
        }
        if (pkt.data)
            av_free_packet(&pkt);

        if (quit) {
            return -1;
        }

        if (packet_queue_get(&audioq, &pkt, 1) < 0) {
            return -1;
        }
        audio_pkt_data = pkt.data;
        audio_pkt_size = pkt.size;
    }

    return 0;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;
    int len1, audio_size;

    static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
    static unsigned int audio_buf_size = 0;
    static unsigned int audio_buf_index = 0;

    while (len > 0) {
        if (audio_buf_index >= audio_buf_size) {
            /* We have already sent all our data; get more */
            audio_size = audio_decode_frame(aCodecCtx, audio_buf,
                    sizeof(audio_buf));
            if (audio_size < 0) {
                /* If error, output silence */
                audio_buf_size = 1024; // arbitrary?
                memset(audio_buf, 0, audio_buf_size);
            } else {
                audio_buf_size = audio_size;
            }
            audio_buf_index = 0;
        }
        len1 = audio_buf_size - audio_buf_index;
        if (len1 > len)
            len1 = len;
        memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, len1);
        len -= len1;
        stream += len1;
        audio_buf_index += len1;
    }
}

int main(int argc, char* args[]) {
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream, audioStream;
    AVCodecContext *pCodecCtx;
    AVCodec *pCodec;
    AVFrame *pFrame;
    AVPacket packet;
    struct SwsContext * pSwsCtx;
    int frameFinished;

    AVCodecContext *aCodecCtx;
    AVCodec *aCodec;

    SDL_Overlay *bmp;
    SDL_Surface *screen;
    SDL_Rect rect;
    SDL_Event event;
    SDL_AudioSpec wanted_spec, spec;

    char filePath[] = "./src/a.mp4";

    // Register all formats and codecs
    av_register_all();

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {
        fprintf(stderr, "Could not initialize SDL - %s
", SDL_GetError());
        exit(1);
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, filePath, NULL, NULL) != 0)
        return -1; // Couldn't open file

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
        return -1; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, filePath, 0);

    // Find the first video stream
    videoStream = -1;
    audioStream = -1;
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && videoStream < 0) {
            videoStream = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audioStream < 0) {
            audioStream = i;
        }
    }
    if (videoStream == -1)
        return -1; // Didn't find a video stream
    if (audioStream == -1)
        return -1;

    aCodecCtx = pFormatCtx->streams[audioStream]->codec;
    // Set audio settings from codec info
    wanted_spec.freq = aCodecCtx->sample_rate;
    wanted_spec.format = AUDIO_S16SYS;
    wanted_spec.channels = aCodecCtx->channels;
    wanted_spec.silence = 0;
    wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
    wanted_spec.callback = audio_callback;
    wanted_spec.userdata = aCodecCtx;

    if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {
        fprintf(stderr, "SDL_OpenAudio: %s
", SDL_GetError());
        return -1;
    }
    aCodec = avcodec_find_decoder(aCodecCtx->codec_id);
    if (!aCodec) {
        fprintf(stderr, "Unsupported codec!
");
        return -1;
    }
    avcodec_open2(aCodecCtx, aCodec, NULL);

    // audio_st = pFormatCtx->streams[index]
    packet_queue_init(&audioq);
    SDL_PauseAudio(0);

    // Get a pointer to the codec context for the video stream
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;

    // Find the decoder for the video stream
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == NULL) {
        fprintf(stderr, "Unsupported codec!
");
        return -1; // Codec not found
    }
    // Open codec
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
        return -1; // Could not open codec

    // Allocate video frame
    pFrame = avcodec_alloc_frame();

    pSwsCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
            pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,
            AV_PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);

    // Make a screen to put our video

#ifndef __DARWIN__
    screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);
#else
    screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 24, 0);
#endif
    if (!screen) {
        fprintf(stderr, "SDL: could not set video mode - exiting
");
        exit(1);
    }

    // Allocate a place to put our YUV image on that screen
    bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,
    SDL_YV12_OVERLAY, screen);

    // Read frames and save first five frames to disk
    i = 0;
    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        // Is this a packet from the video stream?
        if (packet.stream_index == videoStream) {
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

            // Did we get a video frame?
            if (frameFinished) {
                SDL_LockYUVOverlay(bmp);

                AVPicture pict;
                pict.data[0] = bmp->pixels[0];
                pict.data[1] = bmp->pixels[2];
                pict.data[2] = bmp->pixels[1];

                pict.linesize[0] = bmp->pitches[0];
                pict.linesize[1] = bmp->pitches[2];
                pict.linesize[2] = bmp->pitches[1];

                // Convert the image into YUV format that SDL uses
                sws_scale(pSwsCtx, (const uint8_t * const *) pFrame->data,
                        pFrame->linesize, 0, pCodecCtx->height, pict.data,
                        pict.linesize);

                SDL_UnlockYUVOverlay(bmp);

                rect.x = 0;
                rect.y = 0;
                rect.w = pCodecCtx->width;
                rect.h = pCodecCtx->height;
                SDL_DisplayYUVOverlay(bmp, &rect);
                av_free_packet(&packet);
            }
        } else if (packet.stream_index == audioStream) {
            packet_queue_put(&audioq, &packet);
        } else {
            av_free_packet(&packet);
        }
        // Free the packet that was allocated by av_read_frame
        SDL_PollEvent(&event);
        switch (event.type) {
        case SDL_QUIT:
            quit = 1;
            SDL_Quit();
            exit(0);
            break;
        default:
            break;
        }

    }

    // Free the YUV frame
    av_free(pFrame);

    // Close the codec
    avcodec_close(pCodecCtx);

    // Close the video file
    avformat_close_input(&pFormatCtx);

    return EXIT_SUCCESS;
}