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书接上回。在调用av_find_stream_info函数分析媒体文件并找到其中的视频流之后，视频流的相关信息被存放在了AVFormatContext结构体实例中。此时AVCodecContext实例所保存的AVCodec仍然为空。该结构体的定义如下：
typedef struct AVCodec {const char *name;//codec名称，如果是解码HEVC的文件，那就是"hevc"const char *long_name;//codec全名，"HEVC(High Efficient Video Coding)"enum AVMediaType type;//当前codec针对的媒体类型，在此为AVMEDIA_TYPE_VIDEOenum AVCodecID id;//codec_id，检索codec的依据/*** Codec capabilities.* see CODEC_CAP_**/int capabilities;const AVRational *supported_framerates; //<span style="font-family: Arial, Helvetica, sans-serif;">当前codec支持的码率</span>const enum AVPixelFormat *pix_fmts; //<span style="font-family: Arial, Helvetica, sans-serif;">当前codec支持的像素格式</span>const int *supported_samplerates; //<span style="font-family: Arial, Helvetica, sans-serif;">当前codec支持的采样速率（audio）</span>const enum AVSampleFormat *sample_fmts; //<span style="font-family: Arial, Helvetica, sans-serif;">当前codec支持的采样格式（audio）</span>const uint64_t *channel_layouts; //<span style="font-family: Arial, Helvetica, sans-serif;">当前codec支持的声道数</span>
#if FF_API_LOWRESuint8_t max_lowres; ///< maximum value for lowres supported by the decoder, no direct access, use av_codec_get_max_lowres()
#endifconst AVClass *priv_class; ///< AVClass for the private contextconst 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 *);/*** Flush buffers.* Will be called when seeking*/void (*flush)(AVCodecContext *);
} AVCodec;AVCodec *avcodec_find_decoder(enum AVCodecID id)
{return find_encdec(id, 0);
}
static AVCodec *find_encdec(enum AVCodecID id, int encoder)
{AVCodec *p, *experimental = NULL;p = first_avcodec;id= remap_deprecated_codec_id(id);while (p) {if ((encoder ? av_codec_is_encoder(p) : av_codec_is_decoder(p)) &&p->id == id) {if (p->capabilities & CODEC_CAP_EXPERIMENTAL && !experimental) {experimental = p;} elsereturn p;}p = p->next;}return experimental;
}
int av_codec_is_decoder(const AVCodec *codec)
{return codec && codec->decode;
}AVCodec ff_hevc_decoder = {.name = "hevc",.long_name = NULL_IF_CONFIG_SMALL("HEVC (High Efficiency Video Coding)"),.type = AVMEDIA_TYPE_VIDEO,.id = AV_CODEC_ID_HEVC,.priv_data_size = sizeof(HEVCContext),.priv_class = &hevc_decoder_class,.init = hevc_decode_init,.close = hevc_decode_free,.decode = hevc_decode_frame,.flush = hevc_decode_flush,.update_thread_context = hevc_update_thread_context,.init_thread_copy = hevc_init_thread_copy,.capabilities = CODEC_CAP_DR1 | CODEC_CAP_DELAY | CODEC_CAP_SLICE_THREADS | CODEC_CAP_FRAME_THREADS,
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