ffmpeg源代码简单分析 ：avcodec_decode_video2()

本文主要是介绍ffmpeg源代码简单分析 ：avcodec_decode_video2()，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

avcodec_decode_video2()的函数实现如下所示：

int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *picture,int *got_picture_ptr,const AVPacket *avpkt)
{AVCodecInternal *avci = avctx->internal;int ret;// copy to ensure we do not change avpktAVPacket tmp = *avpkt;if (!avctx->codec)return AVERROR(EINVAL);if (avctx->codec->type != AVMEDIA_TYPE_VIDEO) {av_log(avctx, AV_LOG_ERROR, "Invalid media type for video\n");return AVERROR(EINVAL);}*got_picture_ptr = 0;if ((avctx->coded_width || avctx->coded_height) && av_image_check_size(avctx->coded_width, avctx->coded_height, 0, avctx))return AVERROR(EINVAL);avcodec_get_frame_defaults(picture);if (!avctx->refcounted_frames)av_frame_unref(&avci->to_free);if ((avctx->codec->capabilities & CODEC_CAP_DELAY) || avpkt->size || (avctx->active_thread_type & FF_THREAD_FRAME)) {int did_split = av_packet_split_side_data(&tmp);apply_param_change(avctx, &tmp);avctx->pkt = &tmp;if (HAVE_THREADS && avctx->active_thread_type & FF_THREAD_FRAME)ret = ff_thread_decode_frame(avctx, picture, got_picture_ptr,&tmp);else {ret = avctx->codec->decode(avctx, picture, got_picture_ptr,&tmp);picture->pkt_dts = avpkt->dts;if(!avctx->has_b_frames){av_frame_set_pkt_pos(picture, avpkt->pos);}//FIXME these should be under if(!avctx->has_b_frames)/* get_buffer is supposed to set frame parameters */if (!(avctx->codec->capabilities & CODEC_CAP_DR1)) {if (!picture->sample_aspect_ratio.num)    picture->sample_aspect_ratio = avctx->sample_aspect_ratio;if (!picture->width)                      picture->width               = avctx->width;if (!picture->height)                     picture->height              = avctx->height;if (picture->format == AV_PIX_FMT_NONE)   picture->format              = avctx->pix_fmt;}}add_metadata_from_side_data(avctx, picture);emms_c(); //needed to avoid an emms_c() call before every return;avctx->pkt = NULL;if (did_split) {av_packet_free_side_data(&tmp);if(ret == tmp.size)ret = avpkt->size;}if (ret < 0 && picture->data[0])av_frame_unref(picture);if (*got_picture_ptr){if (!avctx->refcounted_frames) {avci->to_free = *picture;avci->to_free.extended_data = avci->to_free.data;memset(picture->buf, 0, sizeof(picture->buf));}avctx->frame_number++;av_frame_set_best_effort_timestamp(picture,guess_correct_pts(avctx,picture->pkt_pts,picture->pkt_dts));}} elseret = 0;/* many decoders assign whole AVFrames, thus overwriting extended_data;* make sure it's set correctly */picture->extended_data = picture->data;return ret;
}

该函数的输入和输出参数分别为 const AVPacket *avpkt和 AVFrame *picture，分别表示待解码的码流和解码完成后的音视频信号，函数的核心是 ret = avctx->codec->decode(avctx, picture, got_picture_ptr,  &tmp)，调用预定义好的解码器进行解码。

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