在上文FFmpeg 結構體學習(四)： AVFrame 分析咱們學習了AVFrame結構體的相關內容。本文，咱們將講述一下AVCodec。html
AVCodec是存儲編解碼器信息的結構體。下面咱們來分析一下該結構體裏重要變量的含義和做用。ide
1、源碼整理
首先咱們先看一下結構體AVCodec的定義的結構體源碼(位於libavcodec/avcodec.h)：函數
/* 雷霄驊 * 中國傳媒大學/數字電視技術 * leixiaohua1020@126.com * */ /** * 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 CodecID id; /** * Codec capabilities. * see CODEC_CAP_* */ int capabilities; const AVRational *supported_framerates; ///< array of supported framerates, or NULL if any, array is terminated by {0,0} const enum PixelFormat *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)(AVCodecContext *, uint8_t *buf, int buf_size, void *data); /** * 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 *); /** * Flush buffers. * Will be called when seeking */ void (*flush)(AVCodecContext *); } AVCodec;
2、AVCodec 重點字段
下面說一下最主要的幾個變量：post
const char *name：編解碼器的名字，比較短 const char *long_name：編解碼器的名字，全稱，比較長 enum AVMediaType type：指明瞭類型，是視頻，音頻，仍是字幕 enum AVCodecID id：ID，不重複 const AVRational *supported_framerates：支持的幀率（僅視頻） const enum AVPixelFormat *pix_fmts：支持的像素格式（僅視頻） const int *supported_samplerates：支持的採樣率（僅音頻） const enum AVSampleFormat *sample_fmts：支持的採樣格式（僅音頻） const uint64_t *channel_layouts：支持的聲道數（僅音頻） int priv_data_size：私有數據的大小
詳細介紹幾個變量：學習
1.enum AVMediaType type
AVMediaType定義以下：ui
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 };