AVCodec
typedef struct AVCodec {
/**
* Name of the codec implementation.
* The name is globally unique among encoders and among decoders (but an
* encoder and a decoder can share the same name).
* This is the primary way to find a codec from the user perspective.
*/
const char *name;
/**
* Descriptive name for the codec, meant to be more human readable than name.
* You should use the NULL_IF_CONFIG_SMALL() macro to define it.
*/
const char *long_name;
enum AVMediaType type;
enum AVCodecID id;
/**
* Codec capabilities.
* see AV_CODEC_CAP_*
*/
int capabilities;
const AVRational *supported_framerates; ///< array of supported framerates, or NULL if any, array is terminated by {0,0}
const enum AVPixelFormat *pix_fmts; ///< array of supported pixel formats, or NULL if unknown, array is terminated by -1
const int *supported_samplerates; ///< array of supported audio samplerates, or NULL if unknown, array is terminated by 0
const enum AVSampleFormat *sample_fmts; ///< array of supported sample formats, or NULL if unknown, array is terminated by -1
const uint64_t *channel_layouts; ///< array of support channel layouts, or NULL if unknown. array is terminated by 0
uint8_t max_lowres; ///< maximum value for lowres supported by the decoder
const AVClass *priv_class; ///< AVClass for the private context
const AVProfile *profiles; ///< array of recognized profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN}
/**
* Group name of the codec implementation.
* This is a short symbolic name of the wrapper backing this codec. A
* wrapper uses some kind of external implementation for the codec, such
* as an external library, or a codec implementation provided by the OS or
* the hardware.
* If this field is NULL, this is a builtin, libavcodec native codec.
* If non-NULL, this will be the suffix in AVCodec.name in most cases
* (usually AVCodec.name will be of the form "<codec_name>_<wrapper_name>").
*/
const char *wrapper_name;
/*****************************************************************
* No fields below this line are part of the public API. They
* may not be used outside of libavcodec and can be changed and
* removed at will.
* New public fields should be added right above.
*****************************************************************
*/
int priv_data_size;
struct AVCodec *next;
/**
* @name Frame-level threading support functions
* @{
*/
/**
* If defined, called on thread contexts when they are created.
* If the codec allocates writable tables in init(), re-allocate them here.
* priv_data will be set to a copy of the original.
*/
int (*init_thread_copy)(AVCodecContext *);
/**
* Copy necessary context variables from a previous thread context to the current one.
* If not defined, the next thread will start automatically; otherwise, the codec
* must call ff_thread_finish_setup().
*
* dst and src will (rarely) point to the same context, in which case memcpy should be skipped.
*/
int (*update_thread_context)(AVCodecContext *dst, const AVCodecContext *src);
/** @} */
/**
* Private codec-specific defaults.
*/
const AVCodecDefault *defaults;
/**
* Initialize codec static data, called from avcodec_register().
*
* This is not intended for time consuming operations as it is
* run for every codec regardless of that codec being used.
*/
void (*init_static_data)(struct AVCodec *codec);
int (*init)(AVCodecContext *);
int (*encode_sub)(AVCodecContext *, uint8_t *buf, int buf_size,
const struct AVSubtitle *sub);
/**
* Encode data to an AVPacket.
*
* @param avctx codec context
* @param avpkt output AVPacket (may contain a user-provided buffer)
* @param[in] frame AVFrame containing the raw data to be encoded
* @param[out] got_packet_ptr encoder sets to 0 or 1 to indicate that a
* non-empty packet was returned in avpkt.
* @return 0 on success, negative error code on failure
*/
int (*encode2)(AVCodecContext *avctx, AVPacket *avpkt, const AVFrame *frame,
int *got_packet_ptr);
int (*decode)(AVCodecContext *, void *outdata, int *outdata_size, AVPacket *avpkt);
int (*close)(AVCodecContext *);
/**
* Encode API with decoupled packet/frame dataflow. The API is the
* same as the avcodec_ prefixed APIs (avcodec_send_frame() etc.), except
* that:
* - never called if the codec is closed or the wrong type,
* - if AV_CODEC_CAP_DELAY is not set, drain frames are never sent,
* - only one drain frame is ever passed down,
*/
int (*send_frame)(AVCodecContext *avctx, const AVFrame *frame);
int (*receive_packet)(AVCodecContext *avctx, AVPacket *avpkt);
/**
* Decode API with decoupled packet/frame dataflow. This function is called
* to get one output frame. It should call ff_decode_get_packet() to obtain
* input data.
*/
int (*receive_frame)(AVCodecContext *avctx, AVFrame *frame);
/**
* Flush buffers.
* Will be called when seeking
*/
void (*flush)(AVCodecContext *);
/**
* Internal codec capabilities.
* See FF_CODEC_CAP_* in internal.h
*/
int caps_internal;
/**
* Decoding only, a comma-separated list of bitstream filters to apply to
* packets before decoding.
*/
const char *bsfs;
/**
* Array of pointers to hardware configurations supported by the codec,
* or NULL if no hardware supported. The array is terminated by a NULL
* pointer.
*
* The user can only access this field via avcodec_get_hw_config().
*/
const struct AVCodecHWConfigInternal **hw_configs;
} AVCodec;
成员变量说明
// 成员变量
const char *name；// 编码器名称，avcodec_find_encoder_by_name使用该变量
const char *long_name; //编码器全称
enum AVMediaType type; // 编码音视频类别
enum AVCodecID id; // 编码器唯一id，avcodec_find_encoder使用该变量
const AVRational *supported_frames; // 支持的视频帧率
const enum AVPixelFormat *pix_fts; // 视频像素格式
const int *supported_samplerates; // 支持的音频采样率
const enum AVSampleFormat *sample_fmts; // 音频采样格式
const uint64_t *channel_layouts ; // 音频通道数
int priv_data_size;
const AVClass *priv_data;
struct AVCodec *next; // 链表下一个编码器
// 成员函数
int (*send_frame)(AVCodecContext *avctx, const AVFrame *frame); // avcodec_send_frame调用
int (*receive_packet)(AVCodecContext *avctx, AVPacket *avpkt); // avcodec_recevie_packet调用
int (*receive_frame)(AVCodecContext *avctx, AVFrame *frame); // avcodec_send_packet/avcodec_receive_frame调用
看具体实例更清晰
实例AVCodec ff_aac_encoder
AVCodec ff_aac_encoder = {
.name = "aac", // 简单名字
.long_name = NULL_IF_CONFIG_SMALL("AAC (Advanced Audio Coding)"), // 复杂名字
.type = AVMEDIA_TYPE_AUDIO, // 编码器所属音视频类别(见下方AVMediaType)
.id = AV_CODEC_ID_AAC, // 编码器唯一标示（avcodec.h）
.priv_data_size = sizeof(AACEncContext),
.init = aac_encode_init, // 编码器ctx初始化函数
.encode2 = aac_encode_frame, // 编码frame为packet的函数
.close = aac_encode_end, // 资源清理函数
.defaults = aac_encode_defaults,
.supported_samplerates = mpeg4audio_sample_rates, // 编码器支持的采样率
.caps_internal = FF_CODEC_CAP_INIT_THREADSAFE,
.capabilities = AV_CODEC_CAP_SMALL_LAST_FRAME | AV_CODEC_CAP_DELAY,
.sample_fmts = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_FLTP,
AV_SAMPLE_FMT_NONE }, // 编码器支持的采样格式
.priv_class = &aacenc_class,
};
实例AVCodec ff_libx264_encoder
AVCodec ff_libx264_encoder = {
.name = "libx264",
.long_name = NULL_IF_CONFIG_SMALL("libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"),
.type = AVMEDIA_TYPE_VIDEO,
.id = AV_CODEC_ID_H264,
.priv_data_size = sizeof(X264Context),
.init = X264_init,
.encode2 = X264_frame,
.close = X264_close,
.capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AUTO_THREADS |
AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE,
.priv_class = &x264_class,
.defaults = x264_defaults,
.init_static_data = X264_init_static,
.caps_internal = FF_CODEC_CAP_INIT_CLEANUP,
.wrapper_name = "libx264",
};
AVMediaType
/**
* @addtogroup lavu_media Media Type
* @brief Media Type
*/
enum AVMediaType {
AVMEDIA_TYPE_UNKNOWN = -1, ///< Usually treated as AVMEDIA_TYPE_DATA
AVMEDIA_TYPE_VIDEO,
AVMEDIA_TYPE_AUDIO,
AVMEDIA_TYPE_DATA, ///< Opaque data information usually continuous
AVMEDIA_TYPE_SUBTITLE,
AVMEDIA_TYPE_ATTACHMENT, ///< Opaque data information usually sparse
AVMEDIA_TYPE_NB
};
AVClass
/**
* Describe the class of an AVClass context structure. That is an
* arbitrary struct of which the first field is a pointer to an
* AVClass struct (e.g. AVCodecContext, AVFormatContext etc.).
*/
typedef struct AVClass {
/**
* The name of the class; usually it is the same name as the
* context structure type to which the AVClass is associated.
*/
const char* class_name;
/**
* A pointer to a function which returns the name of a context
* instance ctx associated with the class.
*/
const char* (*item_name)(void* ctx);
/**
* a pointer to the first option specified in the class if any or NULL
*
* @see av_set_default_options()
*/
const struct AVOption *option;
/**
* LIBAVUTIL_VERSION with which this structure was created.
* This is used to allow fields to be added without requiring major
* version bumps everywhere.
*/
int version;
/**
* Offset in the structure where log_level_offset is stored.
* 0 means there is no such variable
*/
int log_level_offset_offset;
/**
* Offset in the structure where a pointer to the parent context for
* logging is stored. For example a decoder could pass its AVCodecContext
* to eval as such a parent context, which an av_log() implementation
* could then leverage to display the parent context.
* The offset can be NULL.
*/
int parent_log_context_offset;
/**
* Return next AVOptions-enabled child or NULL
*/
void* (*child_next)(void *obj, void *prev);
/**
* Return an AVClass corresponding to the next potential
* AVOptions-enabled child.
*
* The difference between child_next and this is that
* child_next iterates over _already existing_ objects, while
* child_class_next iterates over _all possible_ children.
*/
const struct AVClass* (*child_class_next)(const struct AVClass *prev);
/**
* Category used for visualization (like color)
* This is only set if the category is equal for all objects using this class.
* available since version (51 << 16 | 56 << 8 | 100)
*/
AVClassCategory category;
/**
* Callback to return the category.
* available since version (51 << 16 | 59 << 8 | 100)
*/
AVClassCategory (*get_category)(void* ctx);
/**
* Callback to return the supported/allowed ranges.
* available since version (52.12)
*/
int (*query_ranges)(struct AVOptionRanges **, void *obj, const char *key, int flags);
} AVClass;