FFmpeg: AVCodec结构体解析
AVCodec
AVCodec是FFmpeg比较重要的结构体之一，主要用于存储编解码器的信息。
术语
术语链接：
https://blog.csdn.net/qq_25333681/article/details/80088126
结构定义及成员解读
typedef struct AVCodec {
/**
* 编解码器实现的名称。
* 该名称是全局唯一的（但编码器和解码器可以共享名称）。
* 这是从用户角度查找编解码器的主要方式。
*/
const char *name;
/**
* 编解码器的描述性名称，比前面的名称更具可读性。
* 您应该使用NULL_IF_CONFIG_SMALL（）宏来定义它。
*/
const char *long_name;
enum AVMediaType type;//编解码器类型，视频，音频，或者字幕
enum AVCodecID id;//全局唯一的编解码器ID
/**
* Codec capabilities.
* see AV_CODEC_CAP_*
*/
int capabilities;
const AVRational *supported_framerates; ///支持帧率的数组，用于视频
const enum AVPixelFormat *pix_fmts; ///< 支持的像素格式数组，或者如果未知，则为NULL，数组以-1结尾。用于视频
const int *supported_samplerates; ///< 支持的音频采样率数组，或者如果未知，则为NULL，数组以0结尾。用于音频
const enum AVSampleFormat *sample_fmts; ///<支持的采样数组，或者如果未知，则为NULL，数组以-1结尾。用于音频
const uint64_t *channel_layouts; ///< 支持声道数组，如果未知，则为NULL。 数组以0结尾，用于音频
uint8_t max_lowres; ///< maximum value for lowres supported by the decoder
const AVClass *priv_class; ///< 私有上下文的AVClass
const AVProfile *profiles; ///< 已识别配置文件的数组，或者如果未知，则为NULL，数组以{FF_PROFILE_UNKNOWN}结尾
/*****************************************************************
* 以下所有的字段都不是公共API，不可在libavcodec以外使用。以后新增字段都会放在上面。
*****************************************************************
*/
int priv_data_size;//私有数据大小
struct AVCodec *next;
/**
* @name Frame-level threading support functions
* @{
*/
/**
* 如果已定义，则在创建线程上下文时调用它们。
* 如果编解码器在init（）中分配可写表，请在此处重新分配它们。
* priv_data将被设置为原件的副本。
*/
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);
/** @} */
/**
* 私有编解码器默认值。
*/
const AVCodecDefault *defaults;
/**
* 初始化时从avcodec_register（）调用的编解码器静态数据。
*/
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 *);
/**
* Decode/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,
* - AVPacket parameter change side data is applied right before calling
* AVCodec->send_packet,
* - if AV_CODEC_CAP_DELAY is not set, drain packets or frames are never sent,
* - only one drain packet is ever passed down (until the next flush()),
* - a drain AVPacket is always NULL (no need to check for avpkt->size).
*/
int (*send_frame)(AVCodecContext *avctx, const AVFrame *frame);
int (*send_packet)(AVCodecContext *avctx, const AVPacket *avpkt);
int (*receive_frame)(AVCodecContext *avctx, AVFrame *frame);
int (*receive_packet)(AVCodecContext *avctx, AVPacket *avpkt);
/**
* Flush buffers.
* Will be called when seeking
*/
void (*flush)(AVCodecContext *);
/**
* Internal codec capabilities.
* See FF_CODEC_CAP_* in internal.h
*/
int caps_internal;
} AVCodec;AVMediaType
前面的AVCodec结构体解析中，已经说明AVMediaType表示的是编解码器类型，一般为视频、音频或者字幕。
定义如下：
enum AVMediaType {
AVMEDIA_TYPE_UNKNOWN = -1, ///< 通常视为AVMEDIA_TYPE_DATA类型
AVMEDIA_TYPE_VIDEO,//视频
AVMEDIA_TYPE_AUDIO,//音频
AVMEDIA_TYPE_DATA, ///< 不透明的数据信息，通常是连续的。
AVMEDIA_TYPE_SUBTITLE,//字幕
AVMEDIA_TYPE_ATTACHMENT, ///< 不透明的数据信息，通常很不连续
AVMEDIA_TYPE_NB//牛逼（NB）类型？无法理解，谁知道的告诉我啊
};AVCodecID
定义：超长代码，拣极少一部分贴，见名知意
enum AVCodecID {
AV_CODEC_ID_NONE,
/* 视频编解码器 */
AV_CODEC_ID_MPEG1VIDEO,//用于MPEG1
AV_CODEC_ID_MPEG2VIDEO, ///< 用于MPEG-1/2视频解码的首选ID
#if FF_API_XVMC
AV_CODEC_ID_MPEG2VIDEO_XVMC,
#endif /* FF_API_XVMC */
AV_CODEC_ID_H261,
AV_CODEC_ID_H263,
AV_CODEC_ID_MJPEG,
AV_CODEC_ID_MPEG4,
AV_CODEC_ID_WMV1,
AV_CODEC_ID_H264,
AV_CODEC_ID_VP3,
AV_CODEC_ID_VP5,
AV_CODEC_ID_VP6,
AV_CODEC_ID_GIF,
/* PCM 编解码器 */
AV_CODEC_ID_FIRST_AUDIO = 0x10000, ///< A dummy id pointing at the start of audio codecs
/……
};AVPixelFormat
代码依然超长
enum AVPixelFormat {
AV_PIX_FMT_NONE = -1,
AV_PIX_FMT_YUV420P, ///< planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per 2x2 Y samples)
AV_PIX_FMT_YUYV422, ///< packed YUV 4:2:2, 16bpp, Y0 Cb Y1 Cr
AV_PIX_FMT_RGB24, ///< packed RGB 8:8:8, 24bpp, RGBRGB...
AV_PIX_FMT_BGR24, ///< packed RGB 8:8:8, 24bpp, BGRBGR...
AV_PIX_FMT_YUV422P, ///< planar YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples)
AV_PIX_FMT_YUV444P, ///< planar YUV 4:4:4, 24bpp, (1 Cr & Cb sample per 1x1 Y samples)
AV_PIX_FMT_YUV410P, ///< planar YUV 4:1:0, 9bpp, (1 Cr & Cb sample per 4x4 Y samples)
AV_PIX_FMT_YUV411P, ///< planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y
/*
* 略
*/
AV_PIX_FMT_NB ///< number of pixel formats, DO NOT USE THIS if you want to link with shared libav* because the number of formats might differ between versions
};AVSampleFormat
enum AVSampleFormat {
AV_SAMPLE_FMT_NONE = -1,
AV_SAMPLE_FMT_U8, ///< unsigned 8 bits
AV_SAMPLE_FMT_S16, ///< signed 16 bits
AV_SAMPLE_FMT_S32, ///< signed 32 bits
AV_SAMPLE_FMT_FLT, ///< float
AV_SAMPLE_FMT_DBL, ///< double
AV_SAMPLE_FMT_U8P, ///< unsigned 8 bits, planar
AV_SAMPLE_FMT_S16P, ///< signed 16 bits, planar
AV_SAMPLE_FMT_S32P, ///< signed 32 bits, planar
AV_SAMPLE_FMT_FLTP, ///< float, planar
AV_SAMPLE_FMT_DBLP, ///< double, planar
AV_SAMPLE_FMT_S64, ///< signed 64 bits
AV_SAMPLE_FMT_S64P, ///< signed 64 bits, planar
AV_SAMPLE_FMT_NB ///< Number of sample formats. DO NOT USE if linking dynamically
};参考链接
雷大神：https://blog.csdn.net/leixiaohua1020/article/details/14215833