FFmpeg AVCodec

FFmpeg编解码

FFmpeg支持绝大多数视频编解码格式，如何遍历FFmpeg编解码器？

编解码器以链表形式存储，使用av_codec_next() 函数可以获取编解码器指针，当参数为NULL时，获取第一个编解码器指针，循环遍历，获取所有编解码器信息

void avcodecInfo()

{

     av_register_all();

     AVCodec *c_temp = av_codec_next(NULL);

     while(c_temp!=NULL){

         if (c_temp->encode2!=NULL) {

             switch (c_temp->type){

                 case AVMEDIA_TYPE_VIDEO:

                     printf("[video encode] %10s\n", c_temp->name);

                     break;

                 case AVMEDIA_TYPE_AUDIO:

                     printf("[audio encode] %10s\n", c_temp->name);

                     break;

                 default:

                     printf("[other encode] %10s\n", c_temp->name);

                     break;

             }

         }

         c_temp=c_temp->next;

     }

}

AVCodec登场

遍历FFmpeg编解码器的时候，出现了AVCodec，什么是AVCodec？

AVCodec是存储编解码器信息的结构体，包含了编解码器的基本信息，例如编解码器的名称，编解码类型(video or audio)，以及编解码的参数等。下面列举了常用字段：

const char *name; //编解码器名字
const char *long_name; //编解码器全名
enum AVMediaType type; //编解码器类型
enum AVCodecID id; //编解码器ID
const AVRational *supported_framerates; //支持帧率（视频）
const enum AVPixelFormat *pix_fmts; //支持像素格式(视频）
const int *supported_samplerates; //支持音频采样率(音频）
const enum AVSampleFormat *sample_fmts; //支持采样格式(音频)
const uint64_t *channel_layouts; //支持声道数（音频）
const AVClass *priv_class; //私有数据

AVCodec结构体

mpeg2video(video)编码器结构体

pcm_bluray(audio)解码器结构体

注意：在编解码的时候，要设置为编解码器支持的格式，例如给mpeg2video编码器设置pix_fmts为AV_PIX_FMT_NV12，则会报出以下错误：

Error：Specified pixel format nv12 is invalid or not supported

AVCodec结构体内容

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;

关联类型

从AVCodec中，字段除了基本数据类型，还涉及到了其它结构体和枚举，例如AVMediaType，AVCodecID，AVRational，AVPixelFormat，AVSampleFormat，AVClass等。

AVMediaType媒体类型，是视频，音频，字幕等。

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

};

AVCodecID编解码器唯一标识符

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,

    .......

}

AVPixelFormat视频格式，如RGB，YUV等

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,

    ......

}

AVSampleFormat采样格式，其中带P结尾的为平面格式。例如对于双通道音频，设左通道为L，右通道为R，如果是平面格式，在内存中的排列为LLLLLL……RRRRRR……，对于非平面格式，内存中排列为LRLRLRLRLR……

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

};

巴特西

FFmpeg AVCodec

FFmpeg编解码

AVCodec登场

AVCodec结构体

关联类型

最新文章

热门文章