FFmpeg 4.3 音视频-多路H265监控录放C++开发十三：将AVFrame转换成AVPacket。视频编码原理.编码相关api

前提：

从前面的学习我们知道 AVFrame中是最原始的 视频数据，这一节开始我们需要将这个最原始的视频数据 压缩成 AVPacket数据，

我们前面，将YUV数据或者 RGBA 数据装进入了 AVFrame里面，并且在SDL中显示。

也就是说：对于安防项目来说，我们将原始从摄像头数据(YUV,RGB)转换成 AVFrame后，可以直接显示出来。但是如果我们将要数据存储，则要将 AVFrame转成  AVPacket.

视频编码 以及原理

从摄像头得到原始数据 ---- > 像素格式转换---->编码 ------>封装

编码的原因很好理解，YUV数据太大了，我们要编码成 h264，h265 等较小的格式

背后的原理是这样，一个YUV视频是由一张一张YUV图片组成的。

帧内压缩：

我们将一张YUV图片，假设是 1280x728大小的，我们将其划分成16x16的大小，总有一些像素点是一样的，或者接近的，例如下图：

帧间压缩：

假设上述图片是YUV 的第一张图片，第二帧图片是师爷 在讲话，那么第二帧图片可能只是嘴巴变化了一下，那么我们参考第一张图片，去存储第二张图片，就只用存储第二章图片 和 第一张图片不同的地方就好。。在还原的时候，参考第一张图片和差异，通过算法还原，这就叫做帧间压缩

我们这一节将 AVFrame转成 AVPacket，实际上就是编码的过程，

AVPacket 重要函数以及重要结构体成员

FFmpeg存放压缩后的音视频数据的结构体：AVPacket简介，结构体，函数-CSDN博客

从avframe 变成 avpacket 也就是编码，编码相关API

1.查找编码器

/**
 * Find a registered encoder with a matching codec ID.
 *
 * @param id AVCodecID of the requested encoder
 * @return An encoder if one was found, NULL otherwise.
 */

const AVCodec *avcodec_find_encoder(enum AVCodecID id);

如果参数 是 AVCodecID ，那么对应的值如下，重要的为    

AV_CODEC_ID_H264, 

#define AV_CODEC_ID_H265 AV_CODEC_ID_HEVC

enum AVCodecID {AV_CODEC_ID_NONE,/* video codecs */AV_CODEC_ID_MPEG1VIDEO,AV_CODEC_ID_MPEG2VIDEO, ///< preferred ID for MPEG-1/2 video decodingAV_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,AV_CODEC_ID_INDEO3,AV_CODEC_ID_VP3,AV_CODEC_ID_THEORA,AV_CODEC_ID_ASV1,AV_CODEC_ID_ASV2,AV_CODEC_ID_FFV1,AV_CODEC_ID_4XM,AV_CODEC_ID_VCR1,AV_CODEC_ID_CLJR,AV_CODEC_ID_MDEC,AV_CODEC_ID_ROQ,AV_CODEC_ID_INTERPLAY_VIDEO,AV_CODEC_ID_XAN_WC3,AV_CODEC_ID_XAN_WC4,AV_CODEC_ID_RPZA,AV_CODEC_ID_CINEPAK,AV_CODEC_ID_WS_VQA,AV_CODEC_ID_MSRLE,AV_CODEC_ID_MSVIDEO1,AV_CODEC_ID_IDCIN,AV_CODEC_ID_8BPS,AV_CODEC_ID_SMC,AV_CODEC_ID_FLIC,AV_CODEC_ID_TRUEMOTION1,AV_CODEC_ID_VMDVIDEO,AV_CODEC_ID_MSZH,AV_CODEC_ID_ZLIB,AV_CODEC_ID_QTRLE,AV_CODEC_ID_TSCC,AV_CODEC_ID_ULTI,AV_CODEC_ID_QDRAW,AV_CODEC_ID_VIXL,AV_CODEC_ID_QPEG,AV_CODEC_ID_PNG,AV_CODEC_ID_PPM,AV_CODEC_ID_PBM,AV_CODEC_ID_PGM,AV_CODEC_ID_PGMYUV,AV_CODEC_ID_PAM,AV_CODEC_ID_FFVHUFF,AV_CODEC_ID_RV30,AV_CODEC_ID_RV40,AV_CODEC_ID_VC1,AV_CODEC_ID_WMV3,AV_CODEC_ID_LOCO,AV_CODEC_ID_WNV1,AV_CODEC_ID_AASC,AV_CODEC_ID_INDEO2,AV_CODEC_ID_FRAPS,AV_CODEC_ID_TRUEMOTION2,AV_CODEC_ID_BMP,AV_CODEC_ID_CSCD,AV_CODEC_ID_MMVIDEO,AV_CODEC_ID_ZMBV,AV_CODEC_ID_AVS,AV_CODEC_ID_SMACKVIDEO,AV_CODEC_ID_NUV,AV_CODEC_ID_KMVC,AV_CODEC_ID_FLASHSV,AV_CODEC_ID_CAVS,AV_CODEC_ID_JPEG2000,AV_CODEC_ID_VMNC,AV_CODEC_ID_VP5,AV_CODEC_ID_VP6,AV_CODEC_ID_VP6F,AV_CODEC_ID_TARGA,AV_CODEC_ID_DSICINVIDEO,AV_CODEC_ID_TIERTEXSEQVIDEO,AV_CODEC_ID_TIFF,AV_CODEC_ID_GIF,AV_CODEC_ID_DXA,AV_CODEC_ID_DNXHD,AV_CODEC_ID_THP,AV_CODEC_ID_SGI,AV_CODEC_ID_C93,AV_CODEC_ID_BETHSOFTVID,AV_CODEC_ID_PTX,AV_CODEC_ID_TXD,AV_CODEC_ID_VP6A,AV_CODEC_ID_AMV,AV_CODEC_ID_VB,AV_CODEC_ID_PCX,AV_CODEC_ID_SUNRAST,AV_CODEC_ID_INDEO4,AV_CODEC_ID_INDEO5,AV_CODEC_ID_MIMIC,AV_CODEC_ID_RL2,AV_CODEC_ID_ESCAPE124,AV_CODEC_ID_DIRAC,AV_CODEC_ID_BFI,AV_CODEC_ID_CMV,AV_CODEC_ID_MOTIONPIXELS,AV_CODEC_ID_TGV,AV_CODEC_ID_TGQ,AV_CODEC_ID_TQI,AV_CODEC_ID_AURA,AV_CODEC_ID_AURA2,AV_CODEC_ID_V210X,AV_CODEC_ID_TMV,AV_CODEC_ID_V210,AV_CODEC_ID_DPX,AV_CODEC_ID_MAD,AV_CODEC_ID_FRWU,AV_CODEC_ID_FLASHSV2,AV_CODEC_ID_CDGRAPHICS,AV_CODEC_ID_R210,AV_CODEC_ID_ANM,AV_CODEC_ID_BINKVIDEO,AV_CODEC_ID_IFF_ILBM,
#define AV_CODEC_ID_IFF_BYTERUN1 AV_CODEC_ID_IFF_ILBMAV_CODEC_ID_KGV1,AV_CODEC_ID_YOP,AV_CODEC_ID_VP8,AV_CODEC_ID_PICTOR,AV_CODEC_ID_ANSI,AV_CODEC_ID_A64_MULTI,AV_CODEC_ID_A64_MULTI5,AV_CODEC_ID_R10K,AV_CODEC_ID_MXPEG,AV_CODEC_ID_LAGARITH,AV_CODEC_ID_PRORES,AV_CODEC_ID_JV,AV_CODEC_ID_DFA,AV_CODEC_ID_WMV3IMAGE,AV_CODEC_ID_VC1IMAGE,AV_CODEC_ID_UTVIDEO,AV_CODEC_ID_BMV_VIDEO,AV_CODEC_ID_VBLE,AV_CODEC_ID_DXTORY,AV_CODEC_ID_V410,AV_CODEC_ID_XWD,AV_CODEC_ID_CDXL,AV_CODEC_ID_XBM,AV_CODEC_ID_ZEROCODEC,AV_CODEC_ID_MSS1,AV_CODEC_ID_MSA1,AV_CODEC_ID_TSCC2,AV_CODEC_ID_MTS2,AV_CODEC_ID_CLLC,AV_CODEC_ID_MSS2,AV_CODEC_ID_VP9,AV_CODEC_ID_AIC,AV_CODEC_ID_ESCAPE130,AV_CODEC_ID_G2M,AV_CODEC_ID_WEBP,AV_CODEC_ID_HNM4_VIDEO,AV_CODEC_ID_HEVC,
#define AV_CODEC_ID_H265 AV_CODEC_ID_HEVCAV_CODEC_ID_FIC,AV_CODEC_ID_ALIAS_PIX,AV_CODEC_ID_BRENDER_PIX,AV_CODEC_ID_PAF_VIDEO,AV_CODEC_ID_EXR,AV_CODEC_ID_VP7,AV_CODEC_ID_SANM,AV_CODEC_ID_SGIRLE,AV_CODEC_ID_MVC1,AV_CODEC_ID_MVC2,AV_CODEC_ID_HQX,AV_CODEC_ID_TDSC,AV_CODEC_ID_HQ_HQA,AV_CODEC_ID_HAP,AV_CODEC_ID_DDS,AV_CODEC_ID_DXV,AV_CODEC_ID_SCREENPRESSO,AV_CODEC_ID_RSCC,AV_CODEC_ID_AVS2,AV_CODEC_ID_Y41P = 0x8000,AV_CODEC_ID_AVRP,AV_CODEC_ID_012V,AV_CODEC_ID_AVUI,AV_CODEC_ID_AYUV,AV_CODEC_ID_TARGA_Y216,AV_CODEC_ID_V308,AV_CODEC_ID_V408,AV_CODEC_ID_YUV4,AV_CODEC_ID_AVRN,AV_CODEC_ID_CPIA,AV_CODEC_ID_XFACE,AV_CODEC_ID_SNOW,AV_CODEC_ID_SMVJPEG,AV_CODEC_ID_APNG,AV_CODEC_ID_DAALA,AV_CODEC_ID_CFHD,AV_CODEC_ID_TRUEMOTION2RT,AV_CODEC_ID_M101,AV_CODEC_ID_MAGICYUV,AV_CODEC_ID_SHEERVIDEO,AV_CODEC_ID_YLC,AV_CODEC_ID_PSD,AV_CODEC_ID_PIXLET,AV_CODEC_ID_SPEEDHQ,AV_CODEC_ID_FMVC,AV_CODEC_ID_SCPR,AV_CODEC_ID_CLEARVIDEO,AV_CODEC_ID_XPM,AV_CODEC_ID_AV1,AV_CODEC_ID_BITPACKED,AV_CODEC_ID_MSCC,AV_CODEC_ID_SRGC,AV_CODEC_ID_SVG,AV_CODEC_ID_GDV,AV_CODEC_ID_FITS,AV_CODEC_ID_IMM4,AV_CODEC_ID_PROSUMER,AV_CODEC_ID_MWSC,AV_CODEC_ID_WCMV,AV_CODEC_ID_RASC,AV_CODEC_ID_HYMT,AV_CODEC_ID_ARBC,AV_CODEC_ID_AGM,AV_CODEC_ID_LSCR,AV_CODEC_ID_VP4,AV_CODEC_ID_IMM5,AV_CODEC_ID_MVDV,AV_CODEC_ID_MVHA,AV_CODEC_ID_CDTOONS,AV_CODEC_ID_MV30,AV_CODEC_ID_NOTCHLC,AV_CODEC_ID_PFM,/* various PCM "codecs" */AV_CODEC_ID_FIRST_AUDIO = 0x10000,     ///< A dummy id pointing at the start of audio codecsAV_CODEC_ID_PCM_S16LE = 0x10000,AV_CODEC_ID_PCM_S16BE,AV_CODEC_ID_PCM_U16LE,AV_CODEC_ID_PCM_U16BE,AV_CODEC_ID_PCM_S8,AV_CODEC_ID_PCM_U8,AV_CODEC_ID_PCM_MULAW,AV_CODEC_ID_PCM_ALAW,AV_CODEC_ID_PCM_S32LE,AV_CODEC_ID_PCM_S32BE,AV_CODEC_ID_PCM_U32LE,AV_CODEC_ID_PCM_U32BE,AV_CODEC_ID_PCM_S24LE,AV_CODEC_ID_PCM_S24BE,AV_CODEC_ID_PCM_U24LE,AV_CODEC_ID_PCM_U24BE,AV_CODEC_ID_PCM_S24DAUD,AV_CODEC_ID_PCM_ZORK,AV_CODEC_ID_PCM_S16LE_PLANAR,AV_CODEC_ID_PCM_DVD,AV_CODEC_ID_PCM_F32BE,AV_CODEC_ID_PCM_F32LE,AV_CODEC_ID_PCM_F64BE,AV_CODEC_ID_PCM_F64LE,AV_CODEC_ID_PCM_BLURAY,AV_CODEC_ID_PCM_LXF,AV_CODEC_ID_S302M,AV_CODEC_ID_PCM_S8_PLANAR,AV_CODEC_ID_PCM_S24LE_PLANAR,AV_CODEC_ID_PCM_S32LE_PLANAR,AV_CODEC_ID_PCM_S16BE_PLANAR,AV_CODEC_ID_PCM_S64LE = 0x10800,AV_CODEC_ID_PCM_S64BE,AV_CODEC_ID_PCM_F16LE,AV_CODEC_ID_PCM_F24LE,AV_CODEC_ID_PCM_VIDC,/* various ADPCM codecs */AV_CODEC_ID_ADPCM_IMA_QT = 0x11000,AV_CODEC_ID_ADPCM_IMA_WAV,AV_CODEC_ID_ADPCM_IMA_DK3,AV_CODEC_ID_ADPCM_IMA_DK4,AV_CODEC_ID_ADPCM_IMA_WS,AV_CODEC_ID_ADPCM_IMA_SMJPEG,AV_CODEC_ID_ADPCM_MS,AV_CODEC_ID_ADPCM_4XM,AV_CODEC_ID_ADPCM_XA,AV_CODEC_ID_ADPCM_ADX,AV_CODEC_ID_ADPCM_EA,AV_CODEC_ID_ADPCM_G726,AV_CODEC_ID_ADPCM_CT,AV_CODEC_ID_ADPCM_SWF,AV_CODEC_ID_ADPCM_YAMAHA,AV_CODEC_ID_ADPCM_SBPRO_4,AV_CODEC_ID_ADPCM_SBPRO_3,AV_CODEC_ID_ADPCM_SBPRO_2,AV_CODEC_ID_ADPCM_THP,AV_CODEC_ID_ADPCM_IMA_AMV,AV_CODEC_ID_ADPCM_EA_R1,AV_CODEC_ID_ADPCM_EA_R3,AV_CODEC_ID_ADPCM_EA_R2,AV_CODEC_ID_ADPCM_IMA_EA_SEAD,AV_CODEC_ID_ADPCM_IMA_EA_EACS,AV_CODEC_ID_ADPCM_EA_XAS,AV_CODEC_ID_ADPCM_EA_MAXIS_XA,AV_CODEC_ID_ADPCM_IMA_ISS,AV_CODEC_ID_ADPCM_G722,AV_CODEC_ID_ADPCM_IMA_APC,AV_CODEC_ID_ADPCM_VIMA,AV_CODEC_ID_ADPCM_AFC = 0x11800,AV_CODEC_ID_ADPCM_IMA_OKI,AV_CODEC_ID_ADPCM_DTK,AV_CODEC_ID_ADPCM_IMA_RAD,AV_CODEC_ID_ADPCM_G726LE,AV_CODEC_ID_ADPCM_THP_LE,AV_CODEC_ID_ADPCM_PSX,AV_CODEC_ID_ADPCM_AICA,AV_CODEC_ID_ADPCM_IMA_DAT4,AV_CODEC_ID_ADPCM_MTAF,AV_CODEC_ID_ADPCM_AGM,AV_CODEC_ID_ADPCM_ARGO,AV_CODEC_ID_ADPCM_IMA_SSI,AV_CODEC_ID_ADPCM_ZORK,AV_CODEC_ID_ADPCM_IMA_APM,AV_CODEC_ID_ADPCM_IMA_ALP,AV_CODEC_ID_ADPCM_IMA_MTF,AV_CODEC_ID_ADPCM_IMA_CUNNING,/* AMR */AV_CODEC_ID_AMR_NB = 0x12000,AV_CODEC_ID_AMR_WB,/* RealAudio codecs*/AV_CODEC_ID_RA_144 = 0x13000,AV_CODEC_ID_RA_288,/* various DPCM codecs */AV_CODEC_ID_ROQ_DPCM = 0x14000,AV_CODEC_ID_INTERPLAY_DPCM,AV_CODEC_ID_XAN_DPCM,AV_CODEC_ID_SOL_DPCM,AV_CODEC_ID_SDX2_DPCM = 0x14800,AV_CODEC_ID_GREMLIN_DPCM,AV_CODEC_ID_DERF_DPCM,/* audio codecs */AV_CODEC_ID_MP2 = 0x15000,AV_CODEC_ID_MP3, ///< preferred ID for decoding MPEG audio layer 1, 2 or 3AV_CODEC_ID_AAC,AV_CODEC_ID_AC3,AV_CODEC_ID_DTS,AV_CODEC_ID_VORBIS,AV_CODEC_ID_DVAUDIO,AV_CODEC_ID_WMAV1,AV_CODEC_ID_WMAV2,AV_CODEC_ID_MACE3,AV_CODEC_ID_MACE6,AV_CODEC_ID_VMDAUDIO,AV_CODEC_ID_FLAC,AV_CODEC_ID_MP3ADU,AV_CODEC_ID_MP3ON4,AV_CODEC_ID_SHORTEN,AV_CODEC_ID_ALAC,AV_CODEC_ID_WESTWOOD_SND1,AV_CODEC_ID_GSM, ///< as in Berlin toast formatAV_CODEC_ID_QDM2,AV_CODEC_ID_COOK,AV_CODEC_ID_TRUESPEECH,AV_CODEC_ID_TTA,AV_CODEC_ID_SMACKAUDIO,AV_CODEC_ID_QCELP,AV_CODEC_ID_WAVPACK,AV_CODEC_ID_DSICINAUDIO,AV_CODEC_ID_IMC,AV_CODEC_ID_MUSEPACK7,AV_CODEC_ID_MLP,AV_CODEC_ID_GSM_MS, /* as found in WAV */AV_CODEC_ID_ATRAC3,AV_CODEC_ID_APE,AV_CODEC_ID_NELLYMOSER,AV_CODEC_ID_MUSEPACK8,AV_CODEC_ID_SPEEX,AV_CODEC_ID_WMAVOICE,AV_CODEC_ID_WMAPRO,AV_CODEC_ID_WMALOSSLESS,AV_CODEC_ID_ATRAC3P,AV_CODEC_ID_EAC3,AV_CODEC_ID_SIPR,AV_CODEC_ID_MP1,AV_CODEC_ID_TWINVQ,AV_CODEC_ID_TRUEHD,AV_CODEC_ID_MP4ALS,AV_CODEC_ID_ATRAC1,AV_CODEC_ID_BINKAUDIO_RDFT,AV_CODEC_ID_BINKAUDIO_DCT,AV_CODEC_ID_AAC_LATM,AV_CODEC_ID_QDMC,AV_CODEC_ID_CELT,AV_CODEC_ID_G723_1,AV_CODEC_ID_G729,AV_CODEC_ID_8SVX_EXP,AV_CODEC_ID_8SVX_FIB,AV_CODEC_ID_BMV_AUDIO,AV_CODEC_ID_RALF,AV_CODEC_ID_IAC,AV_CODEC_ID_ILBC,AV_CODEC_ID_OPUS,AV_CODEC_ID_COMFORT_NOISE,AV_CODEC_ID_TAK,AV_CODEC_ID_METASOUND,AV_CODEC_ID_PAF_AUDIO,AV_CODEC_ID_ON2AVC,AV_CODEC_ID_DSS_SP,AV_CODEC_ID_CODEC2,AV_CODEC_ID_FFWAVESYNTH = 0x15800,AV_CODEC_ID_SONIC,AV_CODEC_ID_SONIC_LS,AV_CODEC_ID_EVRC,AV_CODEC_ID_SMV,AV_CODEC_ID_DSD_LSBF,AV_CODEC_ID_DSD_MSBF,AV_CODEC_ID_DSD_LSBF_PLANAR,AV_CODEC_ID_DSD_MSBF_PLANAR,AV_CODEC_ID_4GV,AV_CODEC_ID_INTERPLAY_ACM,AV_CODEC_ID_XMA1,AV_CODEC_ID_XMA2,AV_CODEC_ID_DST,AV_CODEC_ID_ATRAC3AL,AV_CODEC_ID_ATRAC3PAL,AV_CODEC_ID_DOLBY_E,AV_CODEC_ID_APTX,AV_CODEC_ID_APTX_HD,AV_CODEC_ID_SBC,AV_CODEC_ID_ATRAC9,AV_CODEC_ID_HCOM,AV_CODEC_ID_ACELP_KELVIN,AV_CODEC_ID_MPEGH_3D_AUDIO,AV_CODEC_ID_SIREN,AV_CODEC_ID_HCA,/* subtitle codecs */AV_CODEC_ID_FIRST_SUBTITLE = 0x17000,          ///< A dummy ID pointing at the start of subtitle codecs.AV_CODEC_ID_DVD_SUBTITLE = 0x17000,AV_CODEC_ID_DVB_SUBTITLE,AV_CODEC_ID_TEXT,  ///< raw UTF-8 textAV_CODEC_ID_XSUB,AV_CODEC_ID_SSA,AV_CODEC_ID_MOV_TEXT,AV_CODEC_ID_HDMV_PGS_SUBTITLE,AV_CODEC_ID_DVB_TELETEXT,AV_CODEC_ID_SRT,AV_CODEC_ID_MICRODVD   = 0x17800,AV_CODEC_ID_EIA_608,AV_CODEC_ID_JACOSUB,AV_CODEC_ID_SAMI,AV_CODEC_ID_REALTEXT,AV_CODEC_ID_STL,AV_CODEC_ID_SUBVIEWER1,AV_CODEC_ID_SUBVIEWER,AV_CODEC_ID_SUBRIP,AV_CODEC_ID_WEBVTT,AV_CODEC_ID_MPL2,AV_CODEC_ID_VPLAYER,AV_CODEC_ID_PJS,AV_CODEC_ID_ASS,AV_CODEC_ID_HDMV_TEXT_SUBTITLE,AV_CODEC_ID_TTML,AV_CODEC_ID_ARIB_CAPTION,/* other specific kind of codecs (generally used for attachments) */AV_CODEC_ID_FIRST_UNKNOWN = 0x18000,           ///< A dummy ID pointing at the start of various fake codecs.AV_CODEC_ID_TTF = 0x18000,AV_CODEC_ID_SCTE_35, ///< Contain timestamp estimated through PCR of program stream.AV_CODEC_ID_EPG,AV_CODEC_ID_BINTEXT    = 0x18800,AV_CODEC_ID_XBIN,AV_CODEC_ID_IDF,AV_CODEC_ID_OTF,AV_CODEC_ID_SMPTE_KLV,AV_CODEC_ID_DVD_NAV,AV_CODEC_ID_TIMED_ID3,AV_CODEC_ID_BIN_DATA,AV_CODEC_ID_PROBE = 0x19000, ///< codec_id is not known (like AV_CODEC_ID_NONE) but lavf should attempt to identify itAV_CODEC_ID_MPEG2TS = 0x20000, /**< _FAKE_ codec to indicate a raw MPEG-2 TS* stream (only used by libavformat) */AV_CODEC_ID_MPEG4SYSTEMS = 0x20001, /**< _FAKE_ codec to indicate a MPEG-4 Systems* stream (only used by libavformat) */AV_CODEC_ID_FFMETADATA = 0x21000,   ///< Dummy codec for streams containing only metadata information.AV_CODEC_ID_WRAPPED_AVFRAME = 0x21001, ///< Passthrough codec, AVFrames wrapped in AVPacket
};

/**
 * Find a registered encoder with the specified name.
 *
 * @param name name of the requested encoder
 * @return An encoder if one was found, NULL otherwise.
 */
 

const AVCodec *avcodec_find_encoder_by_name(const char *name);

 

如果是通过字符查找对应的编码器/解码器，我们怎么知道这个字符是啥编码器呢？

libavcodec/allcodecs.c中开头定义了很多支编解码结构体;如:

可以查看具体的某一个，当然有些只是定义，ffmpeg并没有实现，如果要实现需要

/** Provide registration of all codecs, parsers and bitstream filters for libavcodec.* Copyright (c) 2002 Fabrice Bellard** This file is part of FFmpeg.** FFmpeg is free software; you can redistribute it and/or* modify it under the terms of the GNU Lesser General Public* License as published by the Free Software Foundation; either* version 2.1 of the License, or (at your option) any later version.** FFmpeg is distributed in the hope that it will be useful,* but WITHOUT ANY WARRANTY; without even the implied warranty of* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU* Lesser General Public License for more details.** You should have received a copy of the GNU Lesser General Public* License along with FFmpeg; if not, write to the Free Software* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA*//*** @file* Provide registration of all codecs, parsers and bitstream filters for libavcodec.*/#include <stdint.h>
#include <string.h>#include "config.h"
#include "config_components.h"
#include "libavutil/thread.h"
#include "codec.h"
#include "codec_id.h"
#include "codec_internal.h"extern const FFCodec ff_a64multi_encoder;
extern const FFCodec ff_a64multi5_encoder;
extern const FFCodec ff_aasc_decoder;
extern const FFCodec ff_aic_decoder;
extern const FFCodec ff_alias_pix_encoder;
extern const FFCodec ff_alias_pix_decoder;
extern const FFCodec ff_agm_decoder;
extern const FFCodec ff_amv_encoder;
extern const FFCodec ff_amv_decoder;
extern const FFCodec ff_anm_decoder;
extern const FFCodec ff_ansi_decoder;
extern const FFCodec ff_apng_encoder;
extern const FFCodec ff_apng_decoder;
extern const FFCodec ff_arbc_decoder;
extern const FFCodec ff_argo_decoder;
extern const FFCodec ff_asv1_encoder;
extern const FFCodec ff_asv1_decoder;
extern const FFCodec ff_asv2_encoder;
extern const FFCodec ff_asv2_decoder;
extern const FFCodec ff_aura_decoder;
extern const FFCodec ff_aura2_decoder;
extern const FFCodec ff_avrp_encoder;
extern const FFCodec ff_avrp_decoder;
extern const FFCodec ff_avrn_decoder;
extern const FFCodec ff_avs_decoder;
extern const FFCodec ff_avui_encoder;
extern const FFCodec ff_avui_decoder;
#if FF_API_AYUV_CODECID
extern const FFCodec ff_ayuv_encoder;
extern const FFCodec ff_ayuv_decoder;
#endif
extern const FFCodec ff_bethsoftvid_decoder;
extern const FFCodec ff_bfi_decoder;
extern const FFCodec ff_bink_decoder;
extern const FFCodec ff_bitpacked_decoder;
extern const FFCodec ff_bitpacked_encoder;
extern const FFCodec ff_bmp_encoder;
extern const FFCodec ff_bmp_decoder;
extern const FFCodec ff_bmv_video_decoder;
extern const FFCodec ff_brender_pix_decoder;
extern const FFCodec ff_c93_decoder;
extern const FFCodec ff_cavs_decoder;
extern const FFCodec ff_cdgraphics_decoder;
extern const FFCodec ff_cdtoons_decoder;
extern const FFCodec ff_cdxl_decoder;
extern const FFCodec ff_cfhd_encoder;
extern const FFCodec ff_cfhd_decoder;
extern const FFCodec ff_cinepak_encoder;
extern const FFCodec ff_cinepak_decoder;
extern const FFCodec ff_clearvideo_decoder;
extern const FFCodec ff_cljr_encoder;
extern const FFCodec ff_cljr_decoder;
extern const FFCodec ff_cllc_decoder;
extern const FFCodec ff_comfortnoise_encoder;
extern const FFCodec ff_comfortnoise_decoder;
extern const FFCodec ff_cpia_decoder;
extern const FFCodec ff_cri_decoder;
extern const FFCodec ff_cscd_decoder;
extern const FFCodec ff_cyuv_decoder;
extern const FFCodec ff_dds_decoder;
extern const FFCodec ff_dfa_decoder;
extern const FFCodec ff_dirac_decoder;
extern const FFCodec ff_dnxhd_encoder;
extern const FFCodec ff_dnxhd_decoder;
extern const FFCodec ff_dpx_encoder;
extern const FFCodec ff_dpx_decoder;
extern const FFCodec ff_dsicinvideo_decoder;
extern const FFCodec ff_dvaudio_decoder;
extern const FFCodec ff_dvvideo_encoder;
extern const FFCodec ff_dvvideo_decoder;
extern const FFCodec ff_dxa_decoder;
extern const FFCodec ff_dxtory_decoder;
extern const FFCodec ff_dxv_decoder;
extern const FFCodec ff_eacmv_decoder;
extern const FFCodec ff_eamad_decoder;
extern const FFCodec ff_eatgq_decoder;
extern const FFCodec ff_eatgv_decoder;
extern const FFCodec ff_eatqi_decoder;
extern const FFCodec ff_eightbps_decoder;
extern const FFCodec ff_eightsvx_exp_decoder;
extern const FFCodec ff_eightsvx_fib_decoder;
extern const FFCodec ff_escape124_decoder;
extern const FFCodec ff_escape130_decoder;
extern const FFCodec ff_exr_encoder;
extern const FFCodec ff_exr_decoder;
extern const FFCodec ff_ffv1_encoder;
extern const FFCodec ff_ffv1_decoder;
extern const FFCodec ff_ffvhuff_encoder;
extern const FFCodec ff_ffvhuff_decoder;
extern const FFCodec ff_fic_decoder;
extern const FFCodec ff_fits_encoder;
extern const FFCodec ff_fits_decoder;
extern const FFCodec ff_flashsv_encoder;
extern const FFCodec ff_flashsv_decoder;
extern const FFCodec ff_flashsv2_encoder;
extern const FFCodec ff_flashsv2_decoder;
extern const FFCodec ff_flic_decoder;
extern const FFCodec ff_flv_encoder;
extern const FFCodec ff_flv_decoder;
extern const FFCodec ff_fmvc_decoder;
extern const FFCodec ff_fourxm_decoder;
extern const FFCodec ff_fraps_decoder;
extern const FFCodec ff_frwu_decoder;
extern const FFCodec ff_g2m_decoder;
extern const FFCodec ff_gdv_decoder;
extern const FFCodec ff_gem_decoder;
extern const FFCodec ff_gif_encoder;
extern const FFCodec ff_gif_decoder;
extern const FFCodec ff_h261_encoder;
extern const FFCodec ff_h261_decoder;
extern const FFCodec ff_h263_encoder;
extern const FFCodec ff_h263_decoder;
extern const FFCodec ff_h263i_decoder;
extern const FFCodec ff_h263p_encoder;
extern const FFCodec ff_h263p_decoder;
extern const FFCodec ff_h263_v4l2m2m_decoder;
extern const FFCodec ff_h264_decoder;
extern const FFCodec ff_h264_crystalhd_decoder;
extern const FFCodec ff_h264_v4l2m2m_decoder;
extern const FFCodec ff_h264_mediacodec_decoder;
extern const FFCodec ff_h264_mediacodec_encoder;
extern const FFCodec ff_h264_mmal_decoder;
extern const FFCodec ff_h264_qsv_decoder;
extern const FFCodec ff_h264_rkmpp_decoder;
extern const FFCodec ff_hap_encoder;
extern const FFCodec ff_hap_decoder;
extern const FFCodec ff_hevc_decoder;
extern const FFCodec ff_hevc_qsv_decoder;
extern const FFCodec ff_hevc_rkmpp_decoder;
extern const FFCodec ff_hevc_v4l2m2m_decoder;
extern const FFCodec ff_hnm4_video_decoder;
extern const FFCodec ff_hq_hqa_decoder;
extern const FFCodec ff_hqx_decoder;
extern const FFCodec ff_huffyuv_encoder;
extern const FFCodec ff_huffyuv_decoder;
extern const FFCodec ff_hymt_decoder;
extern const FFCodec ff_idcin_decoder;
extern const FFCodec ff_iff_ilbm_decoder;
extern const FFCodec ff_imm4_decoder;
extern const FFCodec ff_imm5_decoder;
extern const FFCodec ff_indeo2_decoder;
extern const FFCodec ff_indeo3_decoder;
extern const FFCodec ff_indeo4_decoder;
extern const FFCodec ff_indeo5_decoder;
extern const FFCodec ff_interplay_video_decoder;
extern const FFCodec ff_ipu_decoder;
extern const FFCodec ff_jpeg2000_encoder;
extern const FFCodec ff_jpeg2000_decoder;
extern const FFCodec ff_jpegls_encoder;
extern const FFCodec ff_jpegls_decoder;
extern const FFCodec ff_jv_decoder;
extern const FFCodec ff_kgv1_decoder;
extern const FFCodec ff_kmvc_decoder;
extern const FFCodec ff_lagarith_decoder;
extern const FFCodec ff_ljpeg_encoder;
extern const FFCodec ff_loco_decoder;
extern const FFCodec ff_lscr_decoder;
extern const FFCodec ff_m101_decoder;
extern const FFCodec ff_magicyuv_encoder;
extern const FFCodec ff_magicyuv_decoder;
extern const FFCodec ff_mdec_decoder;
extern const FFCodec ff_media100_decoder;
extern const FFCodec ff_mimic_decoder;
extern const FFCodec ff_mjpeg_encoder;
extern const FFCodec ff_mjpeg_decoder;
extern const FFCodec ff_mjpegb_decoder;
extern const FFCodec ff_mmvideo_decoder;
extern const FFCodec ff_mobiclip_decoder;
extern const FFCodec ff_motionpixels_decoder;
extern const FFCodec ff_mpeg1video_encoder;
extern const FFCodec ff_mpeg1video_decoder;
extern const FFCodec ff_mpeg2video_encoder;
extern const FFCodec ff_mpeg2video_decoder;
extern const FFCodec ff_mpeg4_encoder;
extern const FFCodec ff_mpeg4_decoder;
extern const FFCodec ff_mpeg4_crystalhd_decoder;
extern const FFCodec ff_mpeg4_v4l2m2m_decoder;
extern const FFCodec ff_mpeg4_mmal_decoder;
extern const FFCodec ff_mpegvideo_decoder;
extern const FFCodec ff_mpeg1_v4l2m2m_decoder;
extern const FFCodec ff_mpeg2_mmal_decoder;
extern const FFCodec ff_mpeg2_crystalhd_decoder;
extern const FFCodec ff_mpeg2_v4l2m2m_decoder;
extern const FFCodec ff_mpeg2_qsv_decoder;
extern const FFCodec ff_mpeg2_mediacodec_decoder;
extern const FFCodec ff_msa1_decoder;
extern const FFCodec ff_mscc_decoder;
extern const FFCodec ff_msmpeg4v1_decoder;
extern const FFCodec ff_msmpeg4v2_encoder;
extern const FFCodec ff_msmpeg4v2_decoder;
extern const FFCodec ff_msmpeg4v3_encoder;
extern const FFCodec ff_msmpeg4v3_decoder;
extern const FFCodec ff_msmpeg4_crystalhd_decoder;
extern const FFCodec ff_msp2_decoder;
extern const FFCodec ff_msrle_decoder;
extern const FFCodec ff_mss1_decoder;
extern const FFCodec ff_mss2_decoder;
extern const FFCodec ff_msvideo1_encoder;
extern const FFCodec ff_msvideo1_decoder;
extern const FFCodec ff_mszh_decoder;
extern const FFCodec ff_mts2_decoder;
extern const FFCodec ff_mv30_decoder;
extern const FFCodec ff_mvc1_decoder;
extern const FFCodec ff_mvc2_decoder;
extern const FFCodec ff_mvdv_decoder;
extern const FFCodec ff_mvha_decoder;
extern const FFCodec ff_mwsc_decoder;
extern const FFCodec ff_mxpeg_decoder;
extern const FFCodec ff_notchlc_decoder;
extern const FFCodec ff_nuv_decoder;
extern const FFCodec ff_paf_video_decoder;
extern const FFCodec ff_pam_encoder;
extern const FFCodec ff_pam_decoder;
extern const FFCodec ff_pbm_encoder;
extern const FFCodec ff_pbm_decoder;
extern const FFCodec ff_pcx_encoder;
extern const FFCodec ff_pcx_decoder;
extern const FFCodec ff_pfm_encoder;
extern const FFCodec ff_pfm_decoder;
extern const FFCodec ff_pgm_encoder;
extern const FFCodec ff_pgm_decoder;
extern const FFCodec ff_pgmyuv_encoder;
extern const FFCodec ff_pgmyuv_decoder;
extern const FFCodec ff_pgx_decoder;
extern const FFCodec ff_phm_encoder;
extern const FFCodec ff_phm_decoder;
extern const FFCodec ff_photocd_decoder;
extern const FFCodec ff_pictor_decoder;
extern const FFCodec ff_pixlet_decoder;
extern const FFCodec ff_png_encoder;
extern const FFCodec ff_png_decoder;
extern const FFCodec ff_ppm_encoder;
extern const FFCodec ff_ppm_decoder;
extern const FFCodec ff_prores_encoder;
extern const FFCodec ff_prores_decoder;
extern const FFCodec ff_prores_aw_encoder;
extern const FFCodec ff_prores_ks_encoder;
extern const FFCodec ff_prosumer_decoder;
extern const FFCodec ff_psd_decoder;
extern const FFCodec ff_ptx_decoder;
extern const FFCodec ff_qdraw_decoder;
extern const FFCodec ff_qoi_encoder;
extern const FFCodec ff_qoi_decoder;
extern const FFCodec ff_qpeg_decoder;
extern const FFCodec ff_qtrle_encoder;
extern const FFCodec ff_qtrle_decoder;
extern const FFCodec ff_r10k_encoder;
extern const FFCodec ff_r10k_decoder;
extern const FFCodec ff_r210_encoder;
extern const FFCodec ff_r210_decoder;
extern const FFCodec ff_rasc_decoder;
extern const FFCodec ff_rawvideo_encoder;
extern const FFCodec ff_rawvideo_decoder;
extern const FFCodec ff_rka_decoder;
extern const FFCodec ff_rl2_decoder;
extern const FFCodec ff_roq_encoder;
extern const FFCodec ff_roq_decoder;
extern const FFCodec ff_rpza_encoder;
extern const FFCodec ff_rpza_decoder;
extern const FFCodec ff_rscc_decoder;
extern const FFCodec ff_rv10_encoder;
extern const FFCodec ff_rv10_decoder;
extern const FFCodec ff_rv20_encoder;
extern const FFCodec ff_rv20_decoder;
extern const FFCodec ff_rv30_decoder;
extern const FFCodec ff_rv40_decoder;
extern const FFCodec ff_s302m_encoder;
extern const FFCodec ff_s302m_decoder;
extern const FFCodec ff_sanm_decoder;
extern const FFCodec ff_scpr_decoder;
extern const FFCodec ff_screenpresso_decoder;
extern const FFCodec ff_sga_decoder;
extern const FFCodec ff_sgi_encoder;
extern const FFCodec ff_sgi_decoder;
extern const FFCodec ff_sgirle_decoder;
extern const FFCodec ff_sheervideo_decoder;
extern const FFCodec ff_simbiosis_imx_decoder;
extern const FFCodec ff_smacker_decoder;
extern const FFCodec ff_smc_encoder;
extern const FFCodec ff_smc_decoder;
extern const FFCodec ff_smvjpeg_decoder;
extern const FFCodec ff_snow_encoder;
extern const FFCodec ff_snow_decoder;
extern const FFCodec ff_sp5x_decoder;
extern const FFCodec ff_speedhq_decoder;
extern const FFCodec ff_speedhq_encoder;
extern const FFCodec ff_speex_decoder;
extern const FFCodec ff_srgc_decoder;
extern const FFCodec ff_sunrast_encoder;
extern const FFCodec ff_sunrast_decoder;
extern const FFCodec ff_svq1_encoder;
extern const FFCodec ff_svq1_decoder;
extern const FFCodec ff_svq3_decoder;
extern const FFCodec ff_targa_encoder;
extern const FFCodec ff_targa_decoder;
extern const FFCodec ff_targa_y216_decoder;
extern const FFCodec ff_tdsc_decoder;
extern const FFCodec ff_theora_decoder;
extern const FFCodec ff_thp_decoder;
extern const FFCodec ff_tiertexseqvideo_decoder;
extern const FFCodec ff_tiff_encoder;
extern const FFCodec ff_tiff_decoder;
extern const FFCodec ff_tmv_decoder;
extern const FFCodec ff_truemotion1_decoder;
extern const FFCodec ff_truemotion2_decoder;
extern const FFCodec ff_truemotion2rt_decoder;
extern const FFCodec ff_tscc_decoder;
extern const FFCodec ff_tscc2_decoder;
extern const FFCodec ff_txd_decoder;
extern const FFCodec ff_ulti_decoder;
extern const FFCodec ff_utvideo_encoder;
extern const FFCodec ff_utvideo_decoder;
extern const FFCodec ff_v210_encoder;
extern const FFCodec ff_v210_decoder;
extern const FFCodec ff_v210x_decoder;
extern const FFCodec ff_v308_encoder;
extern const FFCodec ff_v308_decoder;
extern const FFCodec ff_v408_encoder;
extern const FFCodec ff_v408_decoder;
extern const FFCodec ff_v410_encoder;
extern const FFCodec ff_v410_decoder;
extern const FFCodec ff_vb_decoder;
extern const FFCodec ff_vbn_encoder;
extern const FFCodec ff_vbn_decoder;
extern const FFCodec ff_vble_decoder;
extern const FFCodec ff_vc1_decoder;
extern const FFCodec ff_vc1_crystalhd_decoder;
extern const FFCodec ff_vc1image_decoder;
extern const FFCodec ff_vc1_mmal_decoder;
extern const FFCodec ff_vc1_qsv_decoder;
extern const FFCodec ff_vc1_v4l2m2m_decoder;
extern const FFCodec ff_vc2_encoder;
extern const FFCodec ff_vcr1_decoder;
extern const FFCodec ff_vmdvideo_decoder;
extern const FFCodec ff_vmnc_decoder;
extern const FFCodec ff_vp3_decoder;
extern const FFCodec ff_vp4_decoder;
extern const FFCodec ff_vp5_decoder;
extern const FFCodec ff_vp6_decoder;
extern const FFCodec ff_vp6a_decoder;
extern const FFCodec ff_vp6f_decoder;
extern const FFCodec ff_vp7_decoder;
extern const FFCodec ff_vp8_decoder;
extern const FFCodec ff_vp8_rkmpp_decoder;
extern const FFCodec ff_vp8_v4l2m2m_decoder;
extern const FFCodec ff_vp9_decoder;
extern const FFCodec ff_vp9_rkmpp_decoder;
extern const FFCodec ff_vp9_v4l2m2m_decoder;
extern const FFCodec ff_vqa_decoder;
extern const FFCodec ff_vqc_decoder;
extern const FFCodec ff_wbmp_decoder;
extern const FFCodec ff_wbmp_encoder;
extern const FFCodec ff_webp_decoder;
extern const FFCodec ff_wcmv_decoder;
extern const FFCodec ff_wrapped_avframe_encoder;
extern const FFCodec ff_wrapped_avframe_decoder;
extern const FFCodec ff_wmv1_encoder;
extern const FFCodec ff_wmv1_decoder;
extern const FFCodec ff_wmv2_encoder;
extern const FFCodec ff_wmv2_decoder;
extern const FFCodec ff_wmv3_decoder;
extern const FFCodec ff_wmv3_crystalhd_decoder;
extern const FFCodec ff_wmv3image_decoder;
extern const FFCodec ff_wnv1_decoder;
extern const FFCodec ff_xan_wc3_decoder;
extern const FFCodec ff_xan_wc4_decoder;
extern const FFCodec ff_xbm_encoder;
extern const FFCodec ff_xbm_decoder;
extern const FFCodec ff_xface_encoder;
extern const FFCodec ff_xface_decoder;
extern const FFCodec ff_xl_decoder;
extern const FFCodec ff_xpm_decoder;
extern const FFCodec ff_xwd_encoder;
extern const FFCodec ff_xwd_decoder;
extern const FFCodec ff_y41p_encoder;
extern const FFCodec ff_y41p_decoder;
extern const FFCodec ff_ylc_decoder;
extern const FFCodec ff_yop_decoder;
extern const FFCodec ff_yuv4_encoder;
extern const FFCodec ff_yuv4_decoder;
extern const FFCodec ff_zero12v_decoder;
extern const FFCodec ff_zerocodec_decoder;
extern const FFCodec ff_zlib_encoder;
extern const FFCodec ff_zlib_decoder;
extern const FFCodec ff_zmbv_encoder;
extern const FFCodec ff_zmbv_decoder;/* audio codecs */
extern const FFCodec ff_aac_encoder;
extern const FFCodec ff_aac_decoder;
extern const FFCodec ff_aac_fixed_decoder;
extern const FFCodec ff_aac_latm_decoder;
extern const FFCodec ff_ac3_encoder;
extern const FFCodec ff_ac3_decoder;
extern const FFCodec ff_ac3_fixed_encoder;
extern const FFCodec ff_ac3_fixed_decoder;
extern const FFCodec ff_acelp_kelvin_decoder;
extern const FFCodec ff_alac_encoder;
extern const FFCodec ff_alac_decoder;
extern const FFCodec ff_als_decoder;
extern const FFCodec ff_amrnb_decoder;
extern const FFCodec ff_amrwb_decoder;
extern const FFCodec ff_apac_decoder;
extern const FFCodec ff_ape_decoder;
extern const FFCodec ff_aptx_encoder;
extern const FFCodec ff_aptx_decoder;
extern const FFCodec ff_aptx_hd_encoder;
extern const FFCodec ff_aptx_hd_decoder;
extern const FFCodec ff_atrac1_decoder;
extern const FFCodec ff_atrac3_decoder;
extern const FFCodec ff_atrac3al_decoder;
extern const FFCodec ff_atrac3p_decoder;
extern const FFCodec ff_atrac3pal_decoder;
extern const FFCodec ff_atrac9_decoder;
extern const FFCodec ff_binkaudio_dct_decoder;
extern const FFCodec ff_binkaudio_rdft_decoder;
extern const FFCodec ff_bmv_audio_decoder;
extern const FFCodec ff_bonk_decoder;
extern const FFCodec ff_cook_decoder;
extern const FFCodec ff_dca_encoder;
extern const FFCodec ff_dca_decoder;
extern const FFCodec ff_dfpwm_encoder;
extern const FFCodec ff_dfpwm_decoder;
extern const FFCodec ff_dolby_e_decoder;
extern const FFCodec ff_dsd_lsbf_decoder;
extern const FFCodec ff_dsd_msbf_decoder;
extern const FFCodec ff_dsd_lsbf_planar_decoder;
extern const FFCodec ff_dsd_msbf_planar_decoder;
extern const FFCodec ff_dsicinaudio_decoder;
extern const FFCodec ff_dss_sp_decoder;
extern const FFCodec ff_dst_decoder;
extern const FFCodec ff_eac3_encoder;
extern const FFCodec ff_eac3_decoder;
extern const FFCodec ff_evrc_decoder;
extern const FFCodec ff_fastaudio_decoder;
extern const FFCodec ff_ffwavesynth_decoder;
extern const FFCodec ff_flac_encoder;
extern const FFCodec ff_flac_decoder;
extern const FFCodec ff_ftr_decoder;
extern const FFCodec ff_g723_1_encoder;
extern const FFCodec ff_g723_1_decoder;
extern const FFCodec ff_g729_decoder;
extern const FFCodec ff_gsm_decoder;
extern const FFCodec ff_gsm_ms_decoder;
extern const FFCodec ff_hca_decoder;
extern const FFCodec ff_hcom_decoder;
extern const FFCodec ff_hdr_encoder;
extern const FFCodec ff_hdr_decoder;
extern const FFCodec ff_iac_decoder;
extern const FFCodec ff_ilbc_decoder;
extern const FFCodec ff_imc_decoder;
extern const FFCodec ff_interplay_acm_decoder;
extern const FFCodec ff_mace3_decoder;
extern const FFCodec ff_mace6_decoder;
extern const FFCodec ff_metasound_decoder;
extern const FFCodec ff_misc4_decoder;
extern const FFCodec ff_mlp_encoder;
extern const FFCodec ff_mlp_decoder;
extern const FFCodec ff_mp1_decoder;
extern const FFCodec ff_mp1float_decoder;
extern const FFCodec ff_mp2_encoder;
extern const FFCodec ff_mp2_decoder;
extern const FFCodec ff_mp2float_decoder;
extern const FFCodec ff_mp2fixed_encoder;
extern const FFCodec ff_mp3float_decoder;
extern const FFCodec ff_mp3_decoder;
extern const FFCodec ff_mp3adufloat_decoder;
extern const FFCodec ff_mp3adu_decoder;
extern const FFCodec ff_mp3on4float_decoder;
extern const FFCodec ff_mp3on4_decoder;
extern const FFCodec ff_mpc7_decoder;
extern const FFCodec ff_mpc8_decoder;
extern const FFCodec ff_msnsiren_decoder;
extern const FFCodec ff_nellymoser_encoder;
extern const FFCodec ff_nellymoser_decoder;
extern const FFCodec ff_on2avc_decoder;
extern const FFCodec ff_opus_encoder;
extern const FFCodec ff_opus_decoder;
extern const FFCodec ff_paf_audio_decoder;
extern const FFCodec ff_qcelp_decoder;
extern const FFCodec ff_qdm2_decoder;
extern const FFCodec ff_qdmc_decoder;
extern const FFCodec ff_ra_144_encoder;
extern const FFCodec ff_ra_144_decoder;
extern const FFCodec ff_ra_288_decoder;
extern const FFCodec ff_ralf_decoder;
extern const FFCodec ff_sbc_encoder;
extern const FFCodec ff_sbc_decoder;
extern const FFCodec ff_shorten_decoder;
extern const FFCodec ff_sipr_decoder;
extern const FFCodec ff_siren_decoder;
extern const FFCodec ff_smackaud_decoder;
extern const FFCodec ff_sonic_encoder;
extern const FFCodec ff_sonic_decoder;
extern const FFCodec ff_sonic_ls_encoder;
extern const FFCodec ff_tak_decoder;
extern const FFCodec ff_truehd_encoder;
extern const FFCodec ff_truehd_decoder;
extern const FFCodec ff_truespeech_decoder;
extern const FFCodec ff_tta_encoder;
extern const FFCodec ff_tta_decoder;
extern const FFCodec ff_twinvq_decoder;
extern const FFCodec ff_vmdaudio_decoder;
extern const FFCodec ff_vorbis_encoder;
extern const FFCodec ff_vorbis_decoder;
extern const FFCodec ff_wavarc_decoder;
extern const FFCodec ff_wavpack_encoder;
extern const FFCodec ff_wavpack_decoder;
extern const FFCodec ff_wmalossless_decoder;
extern const FFCodec ff_wmapro_decoder;
extern const FFCodec ff_wmav1_encoder;
extern const FFCodec ff_wmav1_decoder;
extern const FFCodec ff_wmav2_encoder;
extern const FFCodec ff_wmav2_decoder;
extern const FFCodec ff_wmavoice_decoder;
extern const FFCodec ff_ws_snd1_decoder;
extern const FFCodec ff_xma1_decoder;
extern const FFCodec ff_xma2_decoder;/* PCM codecs */
extern const FFCodec ff_pcm_alaw_encoder;
extern const FFCodec ff_pcm_alaw_decoder;
extern const FFCodec ff_pcm_bluray_encoder;
extern const FFCodec ff_pcm_bluray_decoder;
extern const FFCodec ff_pcm_dvd_encoder;
extern const FFCodec ff_pcm_dvd_decoder;
extern const FFCodec ff_pcm_f16le_decoder;
extern const FFCodec ff_pcm_f24le_decoder;
extern const FFCodec ff_pcm_f32be_encoder;
extern const FFCodec ff_pcm_f32be_decoder;
extern const FFCodec ff_pcm_f32le_encoder;
extern const FFCodec ff_pcm_f32le_decoder;
extern const FFCodec ff_pcm_f64be_encoder;
extern const FFCodec ff_pcm_f64be_decoder;
extern const FFCodec ff_pcm_f64le_encoder;
extern const FFCodec ff_pcm_f64le_decoder;
extern const FFCodec ff_pcm_lxf_decoder;
extern const FFCodec ff_pcm_mulaw_encoder;
extern const FFCodec ff_pcm_mulaw_decoder;
extern const FFCodec ff_pcm_s8_encoder;
extern const FFCodec ff_pcm_s8_decoder;
extern const FFCodec ff_pcm_s8_planar_encoder;
extern const FFCodec ff_pcm_s8_planar_decoder;
extern const FFCodec ff_pcm_s16be_encoder;
extern const FFCodec ff_pcm_s16be_decoder;
extern const FFCodec ff_pcm_s16be_planar_encoder;
extern const FFCodec ff_pcm_s16be_planar_decoder;
extern const FFCodec ff_pcm_s16le_encoder;
extern const FFCodec ff_pcm_s16le_decoder;
extern const FFCodec ff_pcm_s16le_planar_encoder;
extern const FFCodec ff_pcm_s16le_planar_decoder;
extern const FFCodec ff_pcm_s24be_encoder;
extern const FFCodec ff_pcm_s24be_decoder;
extern const FFCodec ff_pcm_s24daud_encoder;
extern const FFCodec ff_pcm_s24daud_decoder;
extern const FFCodec ff_pcm_s24le_encoder;
extern const FFCodec ff_pcm_s24le_decoder;
extern const FFCodec ff_pcm_s24le_planar_encoder;
extern const FFCodec ff_pcm_s24le_planar_decoder;
extern const FFCodec ff_pcm_s32be_encoder;
extern const FFCodec ff_pcm_s32be_decoder;
extern const FFCodec ff_pcm_s32le_encoder;
extern const FFCodec ff_pcm_s32le_decoder;
extern const FFCodec ff_pcm_s32le_planar_encoder;
extern const FFCodec ff_pcm_s32le_planar_decoder;
extern const FFCodec ff_pcm_s64be_encoder;
extern const FFCodec ff_pcm_s64be_decoder;
extern const FFCodec ff_pcm_s64le_encoder;
extern const FFCodec ff_pcm_s64le_decoder;
extern const FFCodec ff_pcm_sga_decoder;
extern const FFCodec ff_pcm_u8_encoder;
extern const FFCodec ff_pcm_u8_decoder;
extern const FFCodec ff_pcm_u16be_encoder;
extern const FFCodec ff_pcm_u16be_decoder;
extern const FFCodec ff_pcm_u16le_encoder;
extern const FFCodec ff_pcm_u16le_decoder;
extern const FFCodec ff_pcm_u24be_encoder;
extern const FFCodec ff_pcm_u24be_decoder;
extern const FFCodec ff_pcm_u24le_encoder;
extern const FFCodec ff_pcm_u24le_decoder;
extern const FFCodec ff_pcm_u32be_encoder;
extern const FFCodec ff_pcm_u32be_decoder;
extern const FFCodec ff_pcm_u32le_encoder;
extern const FFCodec ff_pcm_u32le_decoder;
extern const FFCodec ff_pcm_vidc_encoder;
extern const FFCodec ff_pcm_vidc_decoder;/* DPCM codecs */
extern const FFCodec ff_cbd2_dpcm_decoder;
extern const FFCodec ff_derf_dpcm_decoder;
extern const FFCodec ff_gremlin_dpcm_decoder;
extern const FFCodec ff_interplay_dpcm_decoder;
extern const FFCodec ff_roq_dpcm_encoder;
extern const FFCodec ff_roq_dpcm_decoder;
extern const FFCodec ff_sdx2_dpcm_decoder;
extern const FFCodec ff_sol_dpcm_decoder;
extern const FFCodec ff_xan_dpcm_decoder;
extern const FFCodec ff_wady_dpcm_decoder;/* ADPCM codecs */
extern const FFCodec ff_adpcm_4xm_decoder;
extern const FFCodec ff_adpcm_adx_encoder;
extern const FFCodec ff_adpcm_adx_decoder;
extern const FFCodec ff_adpcm_afc_decoder;
extern const FFCodec ff_adpcm_agm_decoder;
extern const FFCodec ff_adpcm_aica_decoder;
extern const FFCodec ff_adpcm_argo_decoder;
extern const FFCodec ff_adpcm_argo_encoder;
extern const FFCodec ff_adpcm_ct_decoder;
extern const FFCodec ff_adpcm_dtk_decoder;
extern const FFCodec ff_adpcm_ea_decoder;
extern const FFCodec ff_adpcm_ea_maxis_xa_decoder;
extern const FFCodec ff_adpcm_ea_r1_decoder;
extern const FFCodec ff_adpcm_ea_r2_decoder;
extern const FFCodec ff_adpcm_ea_r3_decoder;
extern const FFCodec ff_adpcm_ea_xas_decoder;
extern const FFCodec ff_adpcm_g722_encoder;
extern const FFCodec ff_adpcm_g722_decoder;
extern const FFCodec ff_adpcm_g726_encoder;
extern const FFCodec ff_adpcm_g726_decoder;
extern const FFCodec ff_adpcm_g726le_encoder;
extern const FFCodec ff_adpcm_g726le_decoder;
extern const FFCodec ff_adpcm_ima_acorn_decoder;
extern const FFCodec ff_adpcm_ima_amv_decoder;
extern const FFCodec ff_adpcm_ima_amv_encoder;
extern const FFCodec ff_adpcm_ima_alp_decoder;
extern const FFCodec ff_adpcm_ima_alp_encoder;
extern const FFCodec ff_adpcm_ima_apc_decoder;
extern const FFCodec ff_adpcm_ima_apm_decoder;
extern const FFCodec ff_adpcm_ima_apm_encoder;
extern const FFCodec ff_adpcm_ima_cunning_decoder;
extern const FFCodec ff_adpcm_ima_dat4_decoder;
extern const FFCodec ff_adpcm_ima_dk3_decoder;
extern const FFCodec ff_adpcm_ima_dk4_decoder;
extern const FFCodec ff_adpcm_ima_ea_eacs_decoder;
extern const FFCodec ff_adpcm_ima_ea_sead_decoder;
extern const FFCodec ff_adpcm_ima_iss_decoder;
extern const FFCodec ff_adpcm_ima_moflex_decoder;
extern const FFCodec ff_adpcm_ima_mtf_decoder;
extern const FFCodec ff_adpcm_ima_oki_decoder;
extern const FFCodec ff_adpcm_ima_qt_encoder;
extern const FFCodec ff_adpcm_ima_qt_decoder;
extern const FFCodec ff_adpcm_ima_rad_decoder;
extern const FFCodec ff_adpcm_ima_ssi_decoder;
extern const FFCodec ff_adpcm_ima_ssi_encoder;
extern const FFCodec ff_adpcm_ima_smjpeg_decoder;
extern const FFCodec ff_adpcm_ima_wav_encoder;
extern const FFCodec ff_adpcm_ima_wav_decoder;
extern const FFCodec ff_adpcm_ima_ws_encoder;
extern const FFCodec ff_adpcm_ima_ws_decoder;
extern const FFCodec ff_adpcm_ms_encoder;
extern const FFCodec ff_adpcm_ms_decoder;
extern const FFCodec ff_adpcm_mtaf_decoder;
extern const FFCodec ff_adpcm_psx_decoder;
extern const FFCodec ff_adpcm_sbpro_2_decoder;
extern const FFCodec ff_adpcm_sbpro_3_decoder;
extern const FFCodec ff_adpcm_sbpro_4_decoder;
extern const FFCodec ff_adpcm_swf_encoder;
extern const FFCodec ff_adpcm_swf_decoder;
extern const FFCodec ff_adpcm_thp_decoder;
extern const FFCodec ff_adpcm_thp_le_decoder;
extern const FFCodec ff_adpcm_vima_decoder;
extern const FFCodec ff_adpcm_xa_decoder;
extern const FFCodec ff_adpcm_xmd_decoder;
extern const FFCodec ff_adpcm_yamaha_encoder;
extern const FFCodec ff_adpcm_yamaha_decoder;
extern const FFCodec ff_adpcm_zork_decoder;/* subtitles */
extern const FFCodec ff_ssa_encoder;
extern const FFCodec ff_ssa_decoder;
extern const FFCodec ff_ass_encoder;
extern const FFCodec ff_ass_decoder;
extern const FFCodec ff_ccaption_decoder;
extern const FFCodec ff_dvbsub_encoder;
extern const FFCodec ff_dvbsub_decoder;
extern const FFCodec ff_dvdsub_encoder;
extern const FFCodec ff_dvdsub_decoder;
extern const FFCodec ff_jacosub_decoder;
extern const FFCodec ff_microdvd_decoder;
extern const FFCodec ff_movtext_encoder;
extern const FFCodec ff_movtext_decoder;
extern const FFCodec ff_mpl2_decoder;
extern const FFCodec ff_pgssub_decoder;
extern const FFCodec ff_pjs_decoder;
extern const FFCodec ff_realtext_decoder;
extern const FFCodec ff_sami_decoder;
extern const FFCodec ff_srt_encoder;
extern const FFCodec ff_srt_decoder;
extern const FFCodec ff_stl_decoder;
extern const FFCodec ff_subrip_encoder;
extern const FFCodec ff_subrip_decoder;
extern const FFCodec ff_subviewer_decoder;
extern const FFCodec ff_subviewer1_decoder;
extern const FFCodec ff_text_encoder;
extern const FFCodec ff_text_decoder;
extern const FFCodec ff_ttml_encoder;
extern const FFCodec ff_vplayer_decoder;
extern const FFCodec ff_webvtt_encoder;
extern const FFCodec ff_webvtt_decoder;
extern const FFCodec ff_xsub_encoder;
extern const FFCodec ff_xsub_decoder;/* external libraries */
extern const FFCodec ff_aac_at_encoder;
extern const FFCodec ff_aac_at_decoder;
extern const FFCodec ff_ac3_at_decoder;
extern const FFCodec ff_adpcm_ima_qt_at_decoder;
extern const FFCodec ff_alac_at_encoder;
extern const FFCodec ff_alac_at_decoder;
extern const FFCodec ff_amr_nb_at_decoder;
extern const FFCodec ff_eac3_at_decoder;
extern const FFCodec ff_gsm_ms_at_decoder;
extern const FFCodec ff_ilbc_at_encoder;
extern const FFCodec ff_ilbc_at_decoder;
extern const FFCodec ff_mp1_at_decoder;
extern const FFCodec ff_mp2_at_decoder;
extern const FFCodec ff_mp3_at_decoder;
extern const FFCodec ff_pcm_alaw_at_encoder;
extern const FFCodec ff_pcm_alaw_at_decoder;
extern const FFCodec ff_pcm_mulaw_at_encoder;
extern const FFCodec ff_pcm_mulaw_at_decoder;
extern const FFCodec ff_qdmc_at_decoder;
extern const FFCodec ff_qdm2_at_decoder;
extern FFCodec ff_libaom_av1_encoder;
extern const FFCodec ff_libaribb24_decoder;
extern const FFCodec ff_libcelt_decoder;
extern const FFCodec ff_libcodec2_encoder;
extern const FFCodec ff_libcodec2_decoder;
extern const FFCodec ff_libdav1d_decoder;
extern const FFCodec ff_libdavs2_decoder;
extern const FFCodec ff_libfdk_aac_encoder;
extern const FFCodec ff_libfdk_aac_decoder;
extern const FFCodec ff_libgsm_encoder;
extern const FFCodec ff_libgsm_decoder;
extern const FFCodec ff_libgsm_ms_encoder;
extern const FFCodec ff_libgsm_ms_decoder;
extern const FFCodec ff_libilbc_encoder;
extern const FFCodec ff_libilbc_decoder;
extern const FFCodec ff_libjxl_decoder;
extern const FFCodec ff_libjxl_encoder;
extern const FFCodec ff_libmp3lame_encoder;
extern const FFCodec ff_libopencore_amrnb_encoder;
extern const FFCodec ff_libopencore_amrnb_decoder;
extern const FFCodec ff_libopencore_amrwb_decoder;
extern const FFCodec ff_libopenjpeg_encoder;
extern const FFCodec ff_libopenjpeg_decoder;
extern const FFCodec ff_libopus_encoder;
extern const FFCodec ff_libopus_decoder;
extern const FFCodec ff_librav1e_encoder;
extern const FFCodec ff_librsvg_decoder;
extern const FFCodec ff_libshine_encoder;
extern const FFCodec ff_libspeex_encoder;
extern const FFCodec ff_libspeex_decoder;
extern const FFCodec ff_libsvtav1_encoder;
extern const FFCodec ff_libtheora_encoder;
extern const FFCodec ff_libtwolame_encoder;
extern const FFCodec ff_libuavs3d_decoder;
extern const FFCodec ff_libvo_amrwbenc_encoder;
extern const FFCodec ff_libvorbis_encoder;
extern const FFCodec ff_libvorbis_decoder;
extern const FFCodec ff_libvpx_vp8_encoder;
extern const FFCodec ff_libvpx_vp8_decoder;
extern FFCodec ff_libvpx_vp9_encoder;
extern FFCodec ff_libvpx_vp9_decoder;
/* preferred over libwebp */
extern const FFCodec ff_libwebp_anim_encoder;
extern const FFCodec ff_libwebp_encoder;
extern const FFCodec ff_libx262_encoder;
#if CONFIG_LIBX264_ENCODER
#include <x264.h>
#if X264_BUILD < 153
#define LIBX264_CONST
#else
#define LIBX264_CONST const
#endif
extern LIBX264_CONST FFCodec ff_libx264_encoder;
#endif
extern const FFCodec ff_libx264rgb_encoder;
extern FFCodec ff_libx265_encoder;
extern const FFCodec ff_libxavs_encoder;
extern const FFCodec ff_libxavs2_encoder;
extern const FFCodec ff_libxvid_encoder;
extern const FFCodec ff_libzvbi_teletext_decoder;/* text */
extern const FFCodec ff_bintext_decoder;
extern const FFCodec ff_xbin_decoder;
extern const FFCodec ff_idf_decoder;/* external libraries, that shouldn't be used by default if one of the* above is available */
extern const FFCodec ff_aac_mf_encoder;
extern const FFCodec ff_ac3_mf_encoder;
extern const FFCodec ff_h263_v4l2m2m_encoder;
extern const FFCodec ff_libaom_av1_decoder;
/* hwaccel hooks only, so prefer external decoders */
extern const FFCodec ff_av1_decoder;
extern const FFCodec ff_av1_cuvid_decoder;
extern const FFCodec ff_av1_mediacodec_decoder;
extern const FFCodec ff_av1_nvenc_encoder;
extern const FFCodec ff_av1_qsv_decoder;
extern const FFCodec ff_av1_qsv_encoder;
extern const FFCodec ff_av1_amf_encoder;
extern const FFCodec ff_libopenh264_encoder;
extern const FFCodec ff_libopenh264_decoder;
extern const FFCodec ff_h264_amf_encoder;
extern const FFCodec ff_h264_cuvid_decoder;
extern const FFCodec ff_h264_mf_encoder;
extern const FFCodec ff_h264_nvenc_encoder;
extern const FFCodec ff_h264_omx_encoder;
extern const FFCodec ff_h264_qsv_encoder;
extern const FFCodec ff_h264_v4l2m2m_encoder;
extern const FFCodec ff_h264_vaapi_encoder;
extern const FFCodec ff_h264_videotoolbox_encoder;
extern const FFCodec ff_hevc_amf_encoder;
extern const FFCodec ff_hevc_cuvid_decoder;
extern const FFCodec ff_hevc_mediacodec_decoder;
extern const FFCodec ff_hevc_mediacodec_encoder;
extern const FFCodec ff_hevc_mf_encoder;
extern const FFCodec ff_hevc_nvenc_encoder;
extern const FFCodec ff_hevc_qsv_encoder;
extern const FFCodec ff_hevc_v4l2m2m_encoder;
extern const FFCodec ff_hevc_vaapi_encoder;
extern const FFCodec ff_hevc_videotoolbox_encoder;
extern const FFCodec ff_libkvazaar_encoder;
extern const FFCodec ff_mjpeg_cuvid_decoder;
extern const FFCodec ff_mjpeg_qsv_encoder;
extern const FFCodec ff_mjpeg_qsv_decoder;
extern const FFCodec ff_mjpeg_vaapi_encoder;
extern const FFCodec ff_mp3_mf_encoder;
extern const FFCodec ff_mpeg1_cuvid_decoder;
extern const FFCodec ff_mpeg2_cuvid_decoder;
extern const FFCodec ff_mpeg2_qsv_encoder;
extern const FFCodec ff_mpeg2_vaapi_encoder;
extern const FFCodec ff_mpeg4_cuvid_decoder;
extern const FFCodec ff_mpeg4_mediacodec_decoder;
extern const FFCodec ff_mpeg4_omx_encoder;
extern const FFCodec ff_mpeg4_v4l2m2m_encoder;
extern const FFCodec ff_prores_videotoolbox_encoder;
extern const FFCodec ff_vc1_cuvid_decoder;
extern const FFCodec ff_vp8_cuvid_decoder;
extern const FFCodec ff_vp8_mediacodec_decoder;
extern const FFCodec ff_vp8_qsv_decoder;
extern const FFCodec ff_vp8_v4l2m2m_encoder;
extern const FFCodec ff_vp8_vaapi_encoder;
extern const FFCodec ff_vp9_cuvid_decoder;
extern const FFCodec ff_vp9_mediacodec_decoder;
extern const FFCodec ff_vp9_qsv_decoder;
extern const FFCodec ff_vp9_vaapi_encoder;
extern const FFCodec ff_vp9_qsv_encoder;// null codecs
extern const FFCodec ff_vnull_decoder;
extern const FFCodec ff_vnull_encoder;
extern const FFCodec ff_anull_decoder;
extern const FFCodec ff_anull_encoder;// The iterate API is not usable with ossfuzz due to the excessive size of binaries created
#if CONFIG_OSSFUZZ
const FFCodec * codec_list[] = {NULL,NULL,NULL
};
#else
#include "libavcodec/codec_list.c"
#endifstatic AVOnce av_codec_static_init = AV_ONCE_INIT;
static void av_codec_init_static(void)
{for (int i = 0; codec_list[i]; i++) {if (codec_list[i]->init_static_data)codec_list[i]->init_static_data((FFCodec*)codec_list[i]);}
}const AVCodec *av_codec_iterate(void **opaque)
{uintptr_t i = (uintptr_t)*opaque;const FFCodec *c = codec_list[i];ff_thread_once(&av_codec_static_init, av_codec_init_static);if (c) {*opaque = (void*)(i + 1);return &c->p;}return NULL;
}static enum AVCodecID remap_deprecated_codec_id(enum AVCodecID id)
{switch(id){//This is for future deprecatec codec ids, its empty since//last major bump but will fill up again over time, please don't remove itdefault                                         : return id;}
}static const AVCodec *find_codec(enum AVCodecID id, int (*x)(const AVCodec *))
{const AVCodec *p, *experimental = NULL;void *i = 0;id = remap_deprecated_codec_id(id);while ((p = av_codec_iterate(&i))) {if (!x(p))continue;if (p->id == id) {if (p->capabilities & AV_CODEC_CAP_EXPERIMENTAL && !experimental) {experimental = p;} elsereturn p;}}return experimental;
}const AVCodec *avcodec_find_encoder(enum AVCodecID id)
{return find_codec(id, av_codec_is_encoder);
}const AVCodec *avcodec_find_decoder(enum AVCodecID id)
{return find_codec(id, av_codec_is_decoder);
}static const AVCodec *find_codec_by_name(const char *name, int (*x)(const AVCodec *))
{void *i = 0;const AVCodec *p;if (!name)return NULL;while ((p = av_codec_iterate(&i))) {if (!x(p))continue;if (strcmp(name, p->name) == 0)return p;}return NULL;
}const AVCodec *avcodec_find_encoder_by_name(const char *name)
{return find_codec_by_name(name, av_codec_is_encoder);
}const AVCodec *avcodec_find_decoder_by_name(const char *name)
{return find_codec_by_name(name, av_codec_is_decoder);
}

2.通过编码器得到编码器上下文

 AVCodecContext *avcodec_alloc_context3(const AVCodec *codec);

/*** Allocate an AVCodecContext and set its fields to default values. The* resulting struct should be freed with avcodec_free_context().** @param codec if non-NULL, allocate private data and initialize defaults*              for the given codec. It is illegal to then call avcodec_open2()*              with a different codec.*              If NULL, then the codec-specific defaults won't be initialized,*              which may result in suboptimal default settings (this is*              important mainly for encoders, e.g. libx264).** @return An AVCodecContext filled with default values or NULL on failure.*/
AVCodecContext *avcodec_alloc_context3(const AVCodec *codec);

3.通过编码器上下文 打开编码器

int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);

参数：

AVCodecContext *avctx：传递的编码器上下文

const AVCodec *codec：如果我们在 创建编码器的时候，传递的是nullptr，那么这时候就要传递具体的codec

AVDictionary **options：一个包含AVCodecContext和编解码器私有选项的字典。返回时，此对象将填充未找到的选项。（这个红色部分的翻译很二，完全看不懂啥意思，），

重新翻译：（可选）一个包含编解码器特定选项的字符串。 这是一个以key=value形式的选项列表，用,分隔。如果不需要额外的选项，可以直接传递NULL。关于 AVDictionary，很显然，这个AVDictionary是为了AVCodecContext 用的，也就是我们指定的编码器（例如h264）有一些参数需要设置，可以通过AVDictionary设置。

我们有两个疑问在这里：

注意的是通过AVDictionary设置的是 特定编码器特定的参数，如果是通用的参数，avcodec中是有key的，通过avcodec设置就好。

1.怎么知道特定的编码器有哪些参数要设置（例如h264编码器有哪些特殊的参数）

        从这里看出，如果要设置这些参数，首先要明白h264的原理，文件结构，因此这里也很有必要学习x264。 另外这里可以参考如何知道x264的参数，了解x265的参数。

2.如何使用 AVDictionary 设定这些特定的参数

核心就是 使用 av_dict_set 一系列方法。        

这里注意的是：如果有特定的参数，设定到AVDictionary后，才能使用 open。

3.还有一种方法是通过 av_opt_set 设定这些特殊的参数

核心是使用 av_opt_set 一系列方法。

例如 

    /// 恒定速率因子（CRF）av_opt_set_int(c->priv_data, "crf", 23, 0);

/*** Initialize the AVCodecContext to use the given AVCodec. Prior to using this* function the context has to be allocated with avcodec_alloc_context3().** The functions avcodec_find_decoder_by_name(), avcodec_find_encoder_by_name(),* avcodec_find_decoder() and avcodec_find_encoder() provide an easy way for* retrieving a codec.** @note Always call this function before using decoding routines (such as* @ref avcodec_receive_frame()).** @code* av_dict_set(&opts, "b", "2.5M", 0);* codec = avcodec_find_decoder(AV_CODEC_ID_H264);* if (!codec)*     exit(1);** context = avcodec_alloc_context3(codec);** if (avcodec_open2(context, codec, opts) < 0)*     exit(1);* @endcode** @param avctx The context to initialize.* @param codec The codec to open this context for. If a non-NULL codec has been*              previously passed to avcodec_alloc_context3() or*              for this context, then this parameter MUST be either NULL or*              equal to the previously passed codec.* @param options A dictionary filled with AVCodecContext and codec-private options.*                On return this object will be filled with options that were not found.** @return zero on success, a negative value on error* @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(),*      av_dict_set(), av_opt_find().*/
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);

4. 将avframe数据发送给 编码器上下文

int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

当然发送前，avframe里面是要有数据的。

/*** Supply a raw video or audio frame to the encoder. Use avcodec_receive_packet()* to retrieve buffered output packets.** @param avctx     codec context* @param[in] frame AVFrame containing the raw audio or video frame to be encoded.*                  Ownership of the frame remains with the caller, and the*                  encoder will not write to the frame. The encoder may create*                  a reference to the frame data (or copy it if the frame is*                  not reference-counted).*                  It can be NULL, in which case it is considered a flush*                  packet.  This signals the end of the stream. If the encoder*                  still has packets buffered, it will return them after this*                  call. Once flushing mode has been entered, additional flush*                  packets are ignored, and sending frames will return*                  AVERROR_EOF.**                  For audio:*                  If AV_CODEC_CAP_VARIABLE_FRAME_SIZE is set, then each frame*                  can have any number of samples.*                  If it is not set, frame->nb_samples must be equal to*                  avctx->frame_size for all frames except the last.*                  The final frame may be smaller than avctx->frame_size.* @retval 0                 success* @retval AVERROR(EAGAIN)   input is not accepted in the current state - user must*                           read output with avcodec_receive_packet() (once all*                           output is read, the packet should be resent, and the*                           call will not fail with EAGAIN).* @retval AVERROR_EOF       the encoder has been flushed, and no new frames can*                           be sent to it* @retval AVERROR(EINVAL)   codec not opened, it is a decoder, or requires flush* @retval AVERROR(ENOMEM)   failed to add packet to internal queue, or similar* @retval "another negative error code" legitimate encoding errors*/
int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

5.从编码器上下文获得 avpacket

int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);

当然在avpacket 的时候，avpacket的空间是需要分配好的。

注意的是1：一帧avframe发送到 解码器上下文，有可能有好几帧avpacket 被解码器上下文 发送出来。

因此在 avcodec_send_frame 调用后，avcodec_receive_packet需要在一个循环中接受 解码器上下文发送出来的 avpacket。循环结束的条件是：avcodec_receive_packet的返回值，注意的是，这个返回值有好几种情况，要分开处理。

注意的是2：另外，循环结束后，还需要通过 avcodec_send_frame 的第二个参数为null，再刷新一下 编码器上下文的缓存。

注意的是3：在循环中，每次通过 avcodec_receive_packet 获得avpacket之后，还应该将avpacket通过 av_packet_unref 将avpacket的引用计数-1，防止内存泄漏。

/*** Read encoded data from the encoder.** @param avctx codec context* @param avpkt This will be set to a reference-counted packet allocated by the*              encoder. Note that the function will always call*              av_packet_unref(avpkt) before doing anything else.* @retval 0               success* @retval AVERROR(EAGAIN) output is not available in the current state - user must*                         try to send input* @retval AVERROR_EOF     the encoder has been fully flushed, and there will be no*                         more output packets* @retval AVERROR(EINVAL) codec not opened, or it is a decoder* @retval "another negative error code" legitimate encoding errors*/
int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);

6 代码