FFmpeg結構體之AVCodec
阿新 • • 發佈：2018-01-04
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AVCodec字段
AVCodec是存儲編解碼器信息的結構體，主要字段註釋如下：
- const char *name; //編解碼器名字
- const char *long_name; //編解碼器全名
- enum AVMediaType type; //編解碼器類型
- enum AVCodecID id; //編解碼器ID
- const AVRational *supported_framerates; //支持幀率數組（視頻）
- const enum AVPixelFormat *pix_fmts; //支持像素格式數組(視頻）
- const int *supported_samplerates; //支持音頻采樣率數組(音頻）
- const enum AVSampleFormat *sample_fmts; //支持采樣格式數組(音頻)
- const uint64_t *channel_layouts; //支持聲道數（音頻）
- const AVClass *priv_class; //私有數據
AVCodec內容
以mpeg2video編碼器為例，說明結構體的內容：
AVCodec遍歷
編解碼器以鏈表形式存儲，av_codec_next()函數可以獲得指向下一個解碼器的指針，具體參考遍歷AVCodec代碼
常見錯誤
mpeg2video支持的格式有AV_PIX_FMT_YUV420P，AV_PIX_FMT_YUV422P，如果設置為AV_PIX_FMT_NV12
AVCodec *codec = avcodec_find_encoder(AV_CODEC_ID_MPEG2VIDEO);
codecCtx->pix_fmt = AV_PIX_FMT_NV12;Error：Specified pixel format nv12 is invalid or not supported
AVCodec定義
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} /***************************************************************** * 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(). */ 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; } AVCodec;
關聯類型
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
};enum AVCodecID {
AV_CODEC_ID_NONE,
/* video codecs */
AV_CODEC_ID_MPEG1VIDEO,
AV_CODEC_ID_MPEG2VIDEO, ///< preferred ID for MPEG-1/2 video decoding
#if FF_API_XVMC
AV_CODEC_ID_MPEG2VIDEO_XVMC,
#endif /* FF_API_XVMC */
AV_CODEC_ID_H261,
AV_CODEC_ID_H263,
AV_CODEC_ID_RV10,
AV_CODEC_ID_RV20,
AV_CODEC_ID_MJPEG,
AV_CODEC_ID_MJPEGB,
AV_CODEC_ID_LJPEG,
AV_CODEC_ID_SP5X,
AV_CODEC_ID_JPEGLS,
AV_CODEC_ID_MPEG4,
AV_CODEC_ID_RAWVIDEO,
AV_CODEC_ID_MSMPEG4V1,
AV_CODEC_ID_MSMPEG4V2,
.......
}/**
* Rational number (pair of numerator and denominator).
*/
typedef struct AVRational{
int num; ///< Numerator
int den; ///< Denominator
} AVRational;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 samples)
AV_PIX_FMT_GRAY8, ///< Y , 8bpp
AV_PIX_FMT_MONOWHITE, ///< Y , 1bpp, 0 is white, 1 is black, in each byte pixels are ordered from the msb to the lsb
AV_PIX_FMT_MONOBLACK, ///< Y , 1bpp, 0 is black, 1 is white, in each byte pixels are ordered from the msb to the lsb
AV_PIX_FMT_PAL8, ///< 8 bits with AV_PIX_FMT_RGB32 palette
AV_PIX_FMT_YUVJ420P, ///< planar YUV 4:2:0, 12bpp, full scale (JPEG), deprecated in favor of AV_PIX_FMT_YUV420P and setting color_range
AV_PIX_FMT_YUVJ422P, ///< planar YUV 4:2:2, 16bpp, full scale (JPEG), deprecated in favor of AV_PIX_FMT_YUV422P and setting color_range
AV_PIX_FMT_YUVJ444P, ///< planar YUV 4:4:4, 24bpp, full scale (JPEG), deprecated in favor of AV_PIX_FMT_YUV444P and setting color_range
#if FF_API_XVMC
AV_PIX_FMT_XVMC_MPEG2_MC,///< XVideo Motion Acceleration via common packet passing
AV_PIX_FMT_XVMC_MPEG2_IDCT,
AV_PIX_FMT_XVMC = AV_PIX_FMT_XVMC_MPEG2_IDCT,
#endif /* FF_API_XVMC */
AV_PIX_FMT_UYVY422,
......
}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
};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;typedef struct AVProfile {
int profile;
const char *name; ///< short name for the profile
} AVProfile;FFmpeg結構體之AVCodec