此前寫了好幾篇ffmpeg源代碼分析文章,列表如下:
圖解FFMPEG打開媒體的函數avformat_open_input
ffmpeg 源代碼簡單分析 : av_register_all()
ffmpeg 源代碼簡單分析 : avcodec_register_all()
ffmpeg 源代碼簡單分析 : av_read_frame()
ffmpeg 源代碼簡單分析 : avcodec_decode_video2()
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ffmpeg中的avcodec_decode_video2()的作用是解碼一幀視頻數據。輸入一個壓縮編碼的結構體AVPacket,輸出一個解碼後的結構體AVFrame。
查看源代碼之後發現,這個函數竟然十分的簡單,源代碼如下:
- int avcodec_decode_video2(AVCodecContext *avctx, AVFrame *picture,
- int *got_picture_ptr,
- const AVPacket *avpkt)
- {
- int ret;
- // copy to ensure we do not change avpkt
- AVPacket tmp = *avpkt;
- *got_picture_ptr= 0;
- if((avctx->coded_width||avctx->coded_height) && av_image_check_size(avctx->coded_width, avctx->coded_height, 0, avctx))
- return -1;
- 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){
- picture->pkt_pos= avpkt->pos;
- }
- //FIXME these should be under if(!avctx->has_b_frames)
- 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 == PIX_FMT_NONE)
- picture->format = avctx->pix_fmt;
- }
- emms_c(); //needed to avoid an emms_c() call before every return;
- avctx->pkt = NULL;
- if (did_split)
- ff_packet_free_side_data(&tmp);
- if (*got_picture_ptr){
- avctx->frame_number++;
- picture->best_effort_timestamp = guess_correct_pts(avctx,
- picture->pkt_pts,
- picture->pkt_dts);
- }
- }else
- ret= 0;
- return ret;
- }
從代碼中可以看出,通過ret = avctx->codec->decode(avctx, picture, got_picture_ptr,&tmp)這句代碼,調用了相應解碼器的decode()函數,完成了解碼操作。
原文地址:http://blog.csdn.net/leixiaohua1020/article/details/12679719