From e2f8fd4a18f3e5a8fdec69c1c472f76b99b9723c Mon Sep 17 00:00:00 2001 From: wenchao1024 <87457873+wenchao1024@users.noreply.github.com> Date: Thu, 6 Jan 2022 14:43:53 +0800 Subject: [PATCH] =?UTF-8?q?Create=20FFmpeg=20=E7=BB=93=E6=9E=84=E4=BD=93?= =?UTF-8?q?=E5=AD=A6=E4=B9=A0(=E4=BA=94)=EF=BC=9A=20AVCodec=20=E5=88=86?= =?UTF-8?q?=E6=9E=90.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ... 结构体学习(五)： AVCodec 分析.md | 320 ++++++++++++++++++ 1 file changed, 320 insertions(+) create mode 100644 FFmpeg 结构体学习(五)： AVCodec 分析.md diff --git a/FFmpeg 结构体学习(五)： AVCodec 分析.md b/FFmpeg 结构体学习(五)： AVCodec 分析.md new file mode 100644 index 0000000..d948ef5 --- /dev/null +++ b/FFmpeg 结构体学习(五)： AVCodec 分析.md @@ -0,0 +1,320 @@ +AVCodec是存储编解码器信息的结构体。下面我们来分析一下该结构体里重要变量的含义和作用。 + +# 一、源码整理 + +首先我们先看一下结构体AVCodec的定义的结构体源码(位于libavcodec/avcodec.h)： + + + +``` +/* 雷霄骅 + * 中国传媒大学/数字电视技术 + * 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; +``` + + + +# 二、AVCodec 重点字段 + +下面说一下最主要的几个变量： + + + +``` +const char *name：编解码器的名字，比较短 + +const char *long_name：编解码器的名字，全称，比较长 + +enum AVMediaType type：指明了类型，是视频，音频，还是字幕 + +enum AVCodecID id：ID，不重复 + +const AVRational *supported_framerates：支持的帧率（仅视频） + +const enum AVPixelFormat *pix_fmts：支持的像素格式（仅视频） + +const int *supported_samplerates：支持的采样率（仅音频） + +const enum AVSampleFormat *sample_fmts：支持的采样格式（仅音频） + +const uint64_t *channel_layouts：支持的声道数（仅音频） + +int priv_data_size：私有数据的大小 +``` + + + +详细介绍几个变量： + +### 1.enum AVMediaType type + +AVMediaType定义如下： + + + +``` +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 +}; +``` + + + +### 2.enum AVCodecID id + +AVCodecID定义如下： + + + +``` +enum AVCodecID { + AV_CODEC_ID_NONE, + + /* video codecs */ + AV_CODEC_ID_MPEG1VIDEO, + AV_CODEC_ID_MPEG2VIDEO, ///< preferred ID for MPEG-1/2 video decoding + AV_CODEC_ID_MPEG2VIDEO_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, + AV_CODEC_ID_MSMPEG4V3, + AV_CODEC_ID_WMV1, + AV_CODEC_ID_WMV2, + AV_CODEC_ID_H263P, + AV_CODEC_ID_H263I, + AV_CODEC_ID_FLV1, + AV_CODEC_ID_SVQ1, + AV_CODEC_ID_SVQ3, + AV_CODEC_ID_DVVIDEO, + AV_CODEC_ID_HUFFYUV, + AV_CODEC_ID_CYUV, + AV_CODEC_ID_H264, + ... +} +``` + + + +### 3.const enum AVPixelFormat *pix_fmts + +AVPixelFormat定义如下： + + + +``` +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 bit with PIX_FMT_RGB32 palette + AV_PIX_FMT_YUVJ420P, ///< planar YUV 4:2:0, 12bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV420P and setting color_range + AV_PIX_FMT_YUVJ422P, ///< planar YUV 4:2:2, 16bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV422P and setting color_range + AV_PIX_FMT_YUVJ444P, ///< planar YUV 4:4:4, 24bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV444P and setting color_range + AV_PIX_FMT_XVMC_MPEG2_MC,///< XVideo Motion Acceleration via common packet passing + AV_PIX_FMT_XVMC_MPEG2_IDCT, + ...（代码太长，略） +} +``` + + + +### 4.const enum AVSampleFormat *sample_fmts + + + +``` +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_NB ///< Number of sample formats. DO NOT USE if linking dynamically +}; +``` + + + + 每一个编解码器对应一个该结构体，查看一下ffmpeg的源代码，我们可以看一下H.264解码器的结构体如下所示（h264.c）： + + + +``` +AVCodec ff_h264_decoder = { + .name = "h264", + .type = AVMEDIA_TYPE_VIDEO, + .id = CODEC_ID_H264, + .priv_data_size = sizeof(H264Context), + .init = ff_h264_decode_init, + .close = ff_h264_decode_end, + .decode = decode_frame, + .capabilities = /*CODEC_CAP_DRAW_HORIZ_BAND |*/ CODEC_CAP_DR1 | CODEC_CAP_DELAY | + CODEC_CAP_SLICE_THREADS | CODEC_CAP_FRAME_THREADS, + .flush= flush_dpb, + .long_name = NULL_IF_CONFIG_SMALL("H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"), + .init_thread_copy = ONLY_IF_THREADS_ENABLED(decode_init_thread_copy), + .update_thread_context = ONLY_IF_THREADS_ENABLED(decode_update_thread_context), + .profiles = NULL_IF_CONFIG_SMALL(profiles), + .priv_class = &h264_class, +}; +``` + + + +JPEG2000解码器结构体（j2kdec.c）： + + + +``` +AVCodec ff_jpeg2000_decoder = { + .name = "j2k", + .type = AVMEDIA_TYPE_VIDEO, + .id = CODEC_ID_JPEG2000, + .priv_data_size = sizeof(J2kDecoderContext), + .init = j2kdec_init, + .close = decode_end, + .decode = decode_frame, + .capabilities = CODEC_CAP_EXPERIMENTAL, + .long_name = NULL_IF_CONFIG_SMALL("JPEG 2000"), + .pix_fmts = + (const enum PixelFormat[]) {PIX_FMT_GRAY8, PIX_FMT_RGB24, PIX_FMT_NONE} +}; +``` + + + +下面简单介绍一下遍历ffmpeg中的解码器信息的方法（这些解码器以一个链表的形式存储）： + +1.注册所有编解码器：av_register_all(); + +2.声明一个AVCodec类型的指针，比如说AVCodec* first_c; + +3.调用av_codec_next()函数，即可获得指向链表下一个解码器的指针，循环往复可以获得所有解码器的信息。注意，如果想要获得指向第一个解码器的指针，则需要将该函数的参数设置为NULL。