FFMPEG SDK 开发介绍(原创)

来源：http://blog.sina.com.cn/s/blog_62a8419a01016exv.html

本文是作者在使用ffmpeg sdk开发过程中的实际经验，现在与大家分享，欢迎学习交流。

FFMPEG SDK 开发介绍

1.简介:
    ffmpeg是一套可以用来记录、转换数字音频、视频，并能将其转化为流的开源计算机程序。
使用ffmpeg能够完成如下功能:parse,demux,decode,filter(preprocessing),encode,mux,stream和player等.

2.下载和编译:

    下载地址:  http://ffmpeg.org/download.html

    编译:
       1)windows平台static library/shared library, 编译工具:mingw-gcc或者在linux平台下交叉编译(推荐)
       2)linux平台static library/shared library, 编译工具:gcc

    模块:
        libavcodec    - 编码解码器
        libavdevice   - 输入输出设备的支持
        libavfilter   - 视音频滤镜支持
        libavformat   - 视音频等格式的解析
        libavutil     - 工具库
        libpostproc   - 后期效果处理
        libswscale    - 图像颜色、尺寸转换
    
3.SDK介绍和开发(基于ffmpeg 0.8 sdk)
    ffmpeg每部分功能都采用plugin的方式，使用统一的接口调用，这样就能够非常方便的使用和扩展。
    plugin分为几种:muxer,demuxer,protocol,hwaccel,encoder,decoder,parser,bitstream,filter,...
    因此在使用SDK的时候第一步就是注册plugin
    
    avcodec_register_all()  : 注册 hwaccel,encoder,decoder,parser,bitstream
    av_register_all()       : 注册 muxer,demuxer,protocol
    avfilter_register_all() : 注册 滤镜filter
    
    下面根据不同的应用场景，给出主要的代码示例(仅是代码片断，不一定能编译通过):
    
    1)如何获取媒体文件的信息(Parser):
    // 参考V3代码: interface IFileDecoder, media/impl/filedecoderimpl.cpp
    
    {
        av_register_all();
        AVFormatContext * pFormatCtx = NULL;
        int err = 0;
        const char *fileName = "c:\test.mp4";
        err = av_open_input_file(&pFormatCtx, fileName, NULL, 0, NULL);
        if(err != 0)
        {
            // break ;
        }
        err = av_find_stream_info(pFormatCtx);
        if(err < 0)
        {
            // break ;
        }
        for(uint32_t i = 0; i < pFormatCtx->nb_streams; i ++)
        {
            // stream 结构数据
            AVStream *pStream = pFormatCtx->streams[i];
            // 帧率信息
            AVRational frameRate = pStream->r_frame_rate;
            // 时间单位比率
            AVRational timeBase = pStream->time_base;
            // stream duration
            int64_t duration = pStream->duration;
            
            // 获取Codec数据结构
            AVCodecContext *pCodecCtx = pStream->codec;
            AVMediaType codecType = pCodecCtx->codec_type;
           
            CodecID codecId = pCodecCtx->codec_id;
           
            
            if(codecType == AVMEDIA_TYPE_VIDEO)
            {
                // 获取Video基本信息
                int width = pCodecCtx->width;
                int height = pCodecCtx->height;
                PixelFormat pixelFormat = pCodecCtx->pix_fmt;
            }
            else if(codecType == AVMEDIA_TYPE_AUDIO)
            {
                // 获取Audio基本信息
                int channels = pCodecCtx->channels;
                int sample_rate = pCodecCtx->sample_rate;
                AVSampleFormat sampleFmt = pCodecCtx->sample_fmt;
            }
        }
        // 释放
        if(pFormatCtx != NULL)
        {
            av_close_input_file(pFormatCtx);
            pFormatCtx = NULL;
        }    
    }
    
    2)读取sample数据(Read raw sample不解码)
    // 参考V3代码: interface IFileDecoder, media/impl/filedecoderimpl.cpp

    {
        // 参考Parser代码
        // av_register_all();
        // AVFormatContext * pFormatCtx = NULL;
        // err = av_open_input_file(&pFormatCtx, fileName, NULL, 0, NULL);
    
        AVPacket packet;
        av_init_packet(&packet);
        int ret = av_read_frame(pFormatCtx, &packet);
        if(ret >= 0)
        {
            int streamIndex = packet.stream_index;
            AVStream *pStream = pFormatCtx->streams[streamIndex];
            AVCodecContext *pCodecCtx = pStream->codec;
            // 计算timestamp
    
            // 转换时间到1/1000000秒
            AVRational time_base;
            time_base.num = 1;
            time_base.den = 1000000;
            
            // 25.0     1/25,   29.97    1001/30000
            
            // 获取 dts/pts
            const int64_t dts = av_rescale_q(packet.dts, pStream->time_base, time_base);
            const int64_t pts = av_rescale_q(packet.pts, pStream->time_base, time_base);
            uint8_t *data = packet.data;
            int size = packet.size;
            bool isKey = ((packet.flags & AV_PKT_FLAG_KEY) == AV_PKT_FLAG_KEY);    
        }
        av_free_packet(&packet);        
    }
    
    3)解码sample(Video ES=>YUV/RGB,  Audio ES=>PCM)
    // 参考V3代码: interface IVideoDecoder/IAudioDecoder, media/impl/videodecoderimpl.cpp/audiodecoderimpl.cpp
    {
        // 参考Parser,Read raw sample代码
        
        // AVMediaType codecType = pCodecCtx->codec_type;
        AVMediaType codecType = AVMEDIA_TYPE_VIDEO;
        // CodecId codecId = pCodecCtx->codec_id;
        CodecId codecId = CODEC_ID_H264;
        
        // 通过Codec ID查找解码器
        AVCodec *pCodec = avcodec_find_decoder(codecId);
        // 分配codec关联结构
        AVCodecContext *pCodecCtx = avcodec_alloc_context();

        // 设置一些必要的信息
        pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO / AVMEDIA_TYPE_AUDIO;
        pCodecCtx->codec_id   = codecId;

        if(pCodec->capabilities & CODEC_CAP_TRUNCATED)
            pCodecCtx->flags |= CODEC_FLAG_TRUNCATED;

        // 在open codec时要加锁，否则多个codec同时打开时时会出现错误
        gMutexFFmpeg.lock();        
        // 打开Codec
        avcodec_open(pCodecCtx, pCodec);        
        gMutexFFmpeg.unlock();
        
        if(codecType == AVMEDIA_TYPE_VIDEO)
        {
            AVFrame *pSrcFrame = avcodec_alloc_frame();
            AVFrame *pDstFrame = avcodec_alloc_frame();
            
            // 因为内存的原因，所以需要多分配一些数据, FF_INPUT_BUFFER_PADDING_SIZE
            uint8_t *data = ...;
            int size = ...;
    
            while(size > 0))
            {
                AVPacket pkt;
                av_init_packet(&pkt);
                pkt.data  = data;
                pkt.size  = size;

                int frameFinished = 0;
                int bytesDecoded = avcodec_decode_video2(pCodecCtx, pSrcFrame, &frameFinished, &pkt);
                if(bytesDecoded > 0)
                {
                    data += bytesDecoded;
                    size -= bytesDecoded;
                }
                if(frameFinished)
                {
                    int numBytes = avpicture_get_size(pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
                    uint8_t *pBuffer = new uint8_t[numBytes];
                    avpicture_fill((AVPicture *)pDstFrame, pBuffer, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
                    av_picture_copy((AVPicture *)pDstFrame, (AVPicture *)pSrcFrame, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
                    
                    // pBuffer/numBytes/pCodecCtx->pix_fmt : YUV/RGB数据
                    delete []pBuffer;                    
                }
                
                if(bytesDecoded < 0)
                    break ;
            }
            av_free(pSrcFrame);
            av_free(pDstFrame);
        }
        else if(codecType == AVMEDIA_TYPE_AUDIO)
        {
            // 分配解码内存空间
            uint8_t *pBuffer = new uint8_t[AVCODEC_MAX_AUDIO_FRAME_SIZE];
    
            // 因为内存的原因，所以需要多分配一些数据, FF_INPUT_BUFFER_PADDING_SIZE
            uint8_t *data = ...;
            int size = ...;
    
            while(size > 0)
            {
                AVPacket pkt;
                av_init_packet(&pkt);
                pkt.data  = data;
                pkt.size  = size;
                
                int outSize = AVCODEC_MAX_AUDIO_FRAME_SIZE;
                int bytesDecoded = avcodec_decode_audio3(pCodecCtx, (int16_t *)pBuffer, &outSize, &pkt);
                if(bytesDecoded > 0)
                {
                    data += bytesDecoded;
                    size -= bytesDecoded;
                }
                if((bytesDecoded >= 0) && (outSize > 0))
                {
                    // pBuffer/outSize : PCM数据
                    // 格式
                    // pCodecCtx->channels;
                    // pCodecCtx->sample_fmt;
                    // pCodecCtx->sample_rate;
                }                
            }            
        }
        
        gMutexFFmpeg.lock();        
        // 关闭和释放
        avcodec_close(pCodecCtx);
        gMutexFFmpeg.unlock();
        av_free(pCodecCtx);
    }
    
    4)视音频编码(YUV/RGB=>Video ES, PCM=>Audio ES)
    // 参考V3代码: media/videoencoder.cpp/audioencoder.cpp
    {
        // video encode
        avcodec_register_all();
        // 查找编码器
        AVCodec *avCodec = avcodec_find_encoder((CodecID)mConfig.codec);
        AVCodecContext *codecCtx = avcodec_alloc_context();
        codecCtx->codec_type    = AVMEDIA_TYPE_VIDEO;
        codecCtx->codec_id      = (CodecID)mConfig.codec;
        codecCtx->width         = mOutFormat.width;
        codecCtx->height        = mOutFormat.height;
        codecCtx->pix_fmt       = (PixelFormat)mOutFormat.pixelFormat;

        uint32 num = 0;
        uint32 den = 0;
        SampleUtil::FPS2Timescale(mOutFormat.frameRate, num, den);
        codecCtx->time_base.num = num;
        codecCtx->time_base.den = den;        
        codecCtx->bit_rate      = mConfig.bitRate*1000;
        codecCtx->max_b_frames  = 0;
        codecCtx->gop_size      = 100;
        if(codecCtx->codec_id == CODEC_ID_MPEG1VIDEO)
        {
            codecCtx->mb_decision = FF_MB_DECISION_RD;
        }
        else
        {
            codecCtx->mb_decision = FF_MB_DECISION_RD;
        }
        
        avcodec_open(codecCtx, avCodec);
        // 分配编码后的内存，分配为1MB
        mOutputBuffer.resize(1*1024*1024);
        
        AVFrame *pSrcFrame = avcodec_alloc_frame();
        
        avcodec_get_frame_defaults(pSrcFrame);
        int ret = avpicture_fill((AVPicture *)pSrcFrame, (uint8_t *)inData.data, (PixelFormat)mOutFormat.pixelFormat, mOutFormat.width, mOutFormat.height);

        AVRational time_base;
        time_base.num = 1;
        time_base.den = 1000000;
        pSrcFrame->pts = av_rescale_q(inData.dts, time_base, codecCtx->time_base);
        
        int bytesWritten = avcodec_encode_video(codecCtx, (uint8 *)mOutputBuffer.data(), mOutputBuffer.size(),
            isEmpty ? NULL : pSrcFrame);

        outData.data  = (char *)mOutputBuffer.data();
        outData.size  = bytesWritten;
        outData.isKey = (mCodecCtx->coded_frame->key_frame != 0);
    
    
        av_free(pSrcFrame);
        avcodec_close(codecCtx);
        av_free(codecCtx);
        
        
        // audio encode请看audioencoder.cpp 文件        
    }
    
    5)图像格式转换(YUV/RGB <=> YUV/RGB & Resize)
    // 参考代码: media/imageconverter.cpp
    {
        SwsContext *pSwsCtx = NULL;
        
       
        
        // resize 算法
        int swsFlags  = SWS_LANCZOS; // SWS_FAST_BILINEAR;
        // 初始化
        pSwsCtx = sws_getCachedContext(NULL, srcWidth, srcHeight, srcFmt,
            dstWidth, dstHeight, dstFmt, swsFlags, NULL, NULL, NULL);
        
        // 设置数据到结构 AVPicture
        AVPicture avSrcPic;
        AVPicture avDstPic;
        memset(&avSrcPic, 0, sizeof(avSrcPic));
        memset(&avDstPic, 0, sizeof(avDstPic));
        int dstRet = avpicture_fill(&avDstPic, (uint8_t *)pDstBuffer, dstFmt, dstWidth, dstHeight);
      
      {
        // pSrcBuffer - 源数据
        // pDstBuffer - 目标数据
        int srcRet = avpicture_fill(&avSrcPic, (uint8_t *)pSrcBuffer, srcFmt, srcWidth, srcHeight);

        // 执行转换
        sws_scale(pSwsCtx, avSrcPic.data, avSrcPic.linesize, 0, abs(srcHeight), avDstPic.data, avDstPic.linesize);
       }
       
        // 释放
        sws_freeContext(pSwsCtx);
    }
    
    6)封装格式(Muxer, .mp4/.avi/.mkv...)
    // 参考代码: interface IFileWriter, media/impl/filewriterimpl.cpp
    {
        av_register_all();

        AVFormatContext * pFormatCtx;
        avformat_alloc_output_context2(&pFormatCtx, NULL, "mp4", "c:\out.mp4");
        
        {
            // new video stream
            AVStream * avStream = av_new_stream(pFormatCtx, pFormatCtx->nb_streams;
            avcodec_get_context_defaults3(avStream->codec, NULL);

            AVCodecContext *codecCtx = avStream->codec;
            codecCtx->codec_id       = (CodecID)format->codecId;
            codecCtx->codec_type     = AVMEDIA_TYPE_VIDEO;
            codecCtx->width          = format->width;
            codecCtx->height         = format->height;
            codecCtx->bit_rate       = 800000;
            uint32 num = 0;
            uint32 den = 0;
            SampleUtil::FPS2Timescale(format->frameRate, num, den);
            codecCtx->time_base.num  = num;
            codecCtx->time_base.den  = den;
            av_set_pts_info(streamInfo->avStream, 64, num, den);
            
            if(pFormatCtx->oformat->flags & AVFMT_GLOBALHEADER)
            {
                codecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;
            }
            switch(codecCtx->codec_id)
            {
            case CODEC_ID_H264:
                {
                    AVBitStreamFilterContext * avFilter = av_bitstream_filter_init("h264_mp4toannexb");
                }
                break ;
            case CODEC_ID_AAC:
                {
                    codecCtx->frame_size = 1024;
                    AVBitStreamFilterContext * avFilter = av_bitstream_filter_init("aac_adtstoasc");
                }
                break ;
            }
            // 设置解码相关数据, 比如H264要设置:SPS & PPS
            codecCtx->extradata_size = ;// size;
            codecCtx->extradata      = ;// (uint8_t *)av_malloc(size + FF_INPUT_BUFFER_PADDING_SIZE);
        }
        {
            // new stream
            AVStream * avStream = av_new_stream(pFormatCtx, pFormatCtx->nb_streams;
            avcodec_get_context_defaults3(avStream->codec, NULL);
        }
        
        err = av_set_parameters(pFormatCtx, NULL);
        // 以写的方式打开文件
        err = avio_open(&pFormatCtx->pb, "c:\out.mp4", AVIO_FLAG_WRITE);

        // 写文件头信息
        err = av_write_header(pFormatCtx);
        
        {
            const AVRational in_time_base = { 1, 1000000 };
            AVRational out_time_base = avStream->time_base;

            AVPacket pkt = { 0 };
            av_init_packet(&pkt);
            
            pkt.stream_index = streamId; // 流的id
            pkt.data  = ;//(uint8_t *)mediaSample->data();
            pkt.size  = ;//mediaSample->size();
            // 转换dts/pts时间单位  1/1000000=>avStream->time_base
            pkt.dts   = av_rescale_q(mediaSample->dts(), in_time_base, out_time_base);
            pkt.pts   = av_rescale_q(mediaSample->pts(), in_time_base, out_time_base);
            pkt.flags = mediaSample->isKey() ? AV_PKT_FLAG_KEY : 0;

            // 写入一帧数据
            int err = av_interleaved_write_frame(pFormatCtx, &pkt);

            av_free_packet(&pkt);            
        }
                
        // 写文件尾信息
        av_write_trailer(pFormatCtx);
        
        // 释放
        // av_bitstream_filter_close(avFilter);
        avio_close(pFormatCtx->pb);
        avformat_free_context(pFormatCtx);
    }
    
    7)滤镜filter的使用(crop, resize, deinterlace, drawtext, overlay, vflip, ...)
    通过搭建若干个filter可以对视音频进行一系列的处理.
        
     a).Simple filtergraphs:
     
         reencode filter graph:
         _________                        __________              ______________
        |         |                      |          |            |              |
        | decoded |  simple filtergraph  | filtered |  encoder   | encoded data |
        | frames  | -------------------> | frames   | ---------> | packets      |
        |_________|                      |__________|            |______________|
        

        filter graph:
         _______        _____________        _______        _____        ________
        |       |      |             |      |       |      |     |      |        |
        | input | ---> | deinterlace | ---> | scale | ---> | fps | ---> | output |
        |_______|      |_____________|      |_______|      |_____|      |________|
        
        
                int ret = av_vsink_buffer_get_video_buffer_ref(mBufferDstCtx, &picRef, 0);
request_frame


start_frame
draw_slice
end_frame
        
        
    b).Complex filtergraphs:
         _________
        |         |
        | input 0 |                    __________
        |_________|                   |          |
                        _________    /| output 0 |
                      |         |  / |__________|
         _________     | complex | /
        |         |     |         |/
        | input 1 |---->| filter  |
        |_________|     |         |    __________
                       /| graph   |  |          |
                      / |         |   | output 1 |
         _________   /  |_________|    |__________|
        |         | /
        | input 2 |/
        |_________|
        
    
    V3组件中实现的 interface IVideoPreprocess代码示例:
    代码文件:media/impl/videopreprocessimpl.cpp
    
    我们搭建的filter graph:
                                                                                         /1-->pad----
        input-->deinterlace-->fps-->logo remove-->color-->image overlaps-->crop-->resize<-0----------->output
                                                                                         2-->crop---/
                                                                                             
        {
            avcodec_register_all();
            avfilter_register_all();
            
            AVFilterGraph * pFilterGraph = NULL;
            AVFilterContext * pBufferSrcCtx = NULL;
            AVFilterContext * pBufferDstCtx = NULL;
            
            AVFrame * pSrcFrame   = avcodec_alloc_frame();
            AVFrame * pSinkFrame  = avcodec_alloc_frame();
            AVFrame * pDstFrame   = avcodec_alloc_frame();

            // 设定输出格式列表，我们仅支持PIX_FMT_YUV420P
            PixelFormat pix_fmts[] = { PIX_FMT_YUV420P, PIX_FMT_NONE };
            char args[512];
            
            AVFilterContext *lastFilterCtx = NULL;
            
            // 我们使用到的filter,其中"nl_"开头的是我们自己写的filter
            // 输入buffer filter
            AVFilter *bufferFilter     = avfilter_get_by_name("buffer");
            // deinterlace filter, 目前使用yadif filter
            AVFilter *yadifFilter      = avfilter_get_by_name("yadif");
            // 我们自己实现的fps转换filter
            AVFilter *fpsFilter        = avfilter_get_by_name("nl_fps");
            // 我们自己实现的遮logo的filter,支持多个，动态设置，能够设定区间范围
            AVFilter *delogosFilter    = avfilter_get_by_name("nl_delogos");
            // 我们自己实现的调节对比度和亮度的filter
            AVFilter *colorFilter      = avfilter_get_by_name("nl_color");
            // 我们自己实现的叠加图片的filter,支持多个，动态设置，能够设定区间范围
            AVFilter *overlaysFilter   = avfilter_get_by_name("nl_overlays");
            // crop filter
            AVFilter *cropFilter       = avfilter_get_by_name("crop");
            // resize filter
            AVFilter *resizeFilter     = avfilter_get_by_name("scale");
            // 图像扩展filter,可以在图像边界填充特定的颜色
            AVFilter *padFilter        = avfilter_get_by_name("pad");
            // 输出buffer filter
            AVFilter *buffersinkFilter = avfilter_get_by_name("buffersink");

            // 创建graph
            pFilterGraph = avfilter_graph_alloc();

            // 开始创建filter
            
            AVRational tb  = { 1, 1000000 };
            AVRational sar = { 0, 1 };
            // 计算图像宽度比
            av_reduce(&sar.num, &sar.den, mConfig.width, mConfig.height, 1000*1000);

            // 设定 buffer filter的参数
            // w:h:pixfmt:time_base.num:time_base.den:sample_aspect_ratio.num:sample_aspect_ratio.den:sws_param
            sprintf(args, "%d:%d:%d:%d:%d:%d:%d",
                mConfig.width, mConfig.height, mConfig.pixelFormat, tb.num, tb.den, sar.num, sar.den);

            // input filter
            err = avfilter_graph_create_filter(&pBufferSrcCtx,  bufferFilter,  "in", args, NULL, pFilterGraph);
            // 记录前一个filter context
            lastFilterCtx = pBufferSrcCtx;
        
            // 如果需要 deinterlace,则创建 yadif filter,同时和前一个filter进行连接
            // deinterlace : yadif
            if(mConfig.deinterlace > 0)
            {
                if(yadifFilter == NULL)
                    break ;

                // yadif filter的参数
                // mode:parity
                sprintf(args, "%d:%d", 0, -1);

                // 创建filter,同时加入到graph
                AVFilterContext *deinterlaceCtx = NULL;
                err = avfilter_graph_create_filter(&deinterlaceCtx,  yadifFilter, "yadif", args, NULL, pFilterGraph);
                if(err < 0)
                    break ;

                // 和前一个filter进行连接
                err = avfilter_link(lastFilterCtx, 0, deinterlaceCtx, 0);
                if(err < 0)
                    break ;

                lastFilterCtx = deinterlaceCtx;
            }
            // ... 中间略过
                    
            // 创建output filter
            err = avfilter_graph_create_filter(&pBufferDstCtx, buffersinkFilter, "out", NULL, pix_fmts, pFilterGraph);
            if(err < 0)
                break ;
     
            // 和前一个filter进行连接
            err = avfilter_link(lastFilterCtx, 0, pBufferDstCtx, 0);
            if(err < 0)
                break ;
                
            // 配置 graph
            err = avfilter_graph_config(pFilterGraph, NULL);

            
            // 把输入frame填充到结构AVFrame
            avpicture_fill((AVPicture *)pSrcFrame, (uint8_t *)inMediaSample->data(),
                (PixelFormat)mConfig.pixelFormat, mConfig.width, mConfig.height);
            pSrcFrame->width  = mConfig.width;
            pSrcFrame->height = mConfig.height;
            pSrcFrame->format = mConfig.pixelFormat;
            pSrcFrame->pts = inMediaSample->dts();

            // 开始写input写入frame
            ret = av_vsrc_buffer_add_frame(pBufferSrcCtx, pSrcFrame, AV_VSRC_BUF_FLAG_OVERWRITE);
            
            
            // 从输出filter查看输入是否可以获取数据,返回可获取的数目
            int count = avfilter_poll_frame(pBufferDstCtx->inputs[0]);
            if(count > 0)
            {
                AVFilterBufferRef *picRef = NULL;
                // 从输出filter中获取结果
                int ret = av_vsink_buffer_get_video_buffer_ref(pBufferDstCtx, &picRef, 0);
                if(picRef != NULL)
                {
                    // 转换AVFilterBufferRef到AVFrame
                    avfilter_fill_frame_from_video_buffer_ref(pSinkFrame, picRef);
                    pSinkFrame->format = picRef->format;
                    pSinkFrame->width  = picRef->video->w;
                    pSinkFrame->height = picRef->video->h;
                    
                    const int numBytes = avpicture_get_size((PixelFormat)pSinkFrame->format, pSinkFrame->width, pSinkFrame->height);
                    // 转换时间单位
                    AVRational tb  = { 1, 1000000 };
                    const int64 dts = av_rescale_q(picRef->pts, mBufferDstCtx->inputs[0]->time_base, tb);
                    // 获取图像数据
                    avpicture_fill((AVPicture *)pDstFrame, (uint8_t *)mediaSample->data(),
                        (PixelFormat)pSinkFrame->format, pSinkFrame->width, pSinkFrame->height);

                    av_picture_copy((AVPicture *)pDstFrame, (AVPicture *)pSinkFrame,
                        (PixelFormat)pSinkFrame->format, pSinkFrame->width, pSinkFrame->height);                        
                    
                    // 释放buffer计数器
                    avfilter_unref_buffer(picRef);
                }
            }
        }                                                                                         
                                                                                            

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