ffmpeg 之avcodec_receive_frame分析二-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_43360707/article/details/115962764

这段代码涉及AVCodecContext和AVFrame在音视频处理中的应用。主要功能是在解码过程中接收和处理帧数据，包括检查解码状态、格式变化检测以及在接收帧后进行的处理操作，如裁剪和错误处理。代码调用了decode_receive_frame_internal()函数来实际接收解码后的帧，并在视频和音频类型中检查格式变化，以决定是否丢弃已改变的帧。

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直接看代码，我们在一中分析到，在send的时候最后一步就是将gpu中数据拷贝出来（这个过程是异步的），然后在这里读取


int attribute_align_arg avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
{
    AVCodecInternal *avci = avctx->internal;
    int ret, changed;

    av_frame_unref(frame);

    if (!avcodec_is_open(avctx) || !av_codec_is_decoder(avctx->codec))
        return AVERROR(EINVAL);

    if (avci->buffer_frame->buf[0]) {
        av_frame_move_ref(frame, avci->buffer_frame);
    } else {
    //在这里接受数据
        ret = decode_receive_frame_internal(avctx, frame);
        if (ret < 0)
            return ret;
    }

    if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
        ret = apply_cropping(avctx, frame);
        if (ret < 0) {
            av_frame_unref(frame);
            return ret;
        }
    }

    avctx->frame_number++;

    if (avctx->flags & AV_CODEC_FLAG_DROPCHANGED) {

        if (avctx->frame_number == 1) {
            avci->initial_format = frame->format;
            switch(avctx->codec_type) {
            case AVMEDIA_TYPE_VIDEO:
                avci->initial_width  = frame->width;
                avci->initial_height = frame->height;
                break;
            case AVMEDIA_TYPE_AUDIO:
                avci->initial_sample_rate = frame->sample_rate ? frame->sample_rate :
                                                                 avctx->sample_rate;
                avci->initial_channels       = frame->channels;
                avci->initial_channel_layout = frame->channel_layout;
                break;
            }
        }

        if (avctx->frame_number > 1) {
            changed = avci->initial_format != frame->format;

           switch(avctx->codec_type) {
            case AVMEDIA_TYPE_VIDEO:
                changed |= avci->initial_width  != frame->width ||
                           avci->initial_height != frame->height;
                break;
            case AVMEDIA_TYPE_AUDIO:
                changed |= avci->initial_sample_rate    != frame->sample_rate ||
                           avci->initial_sample_rate    != avctx->sample_rate ||
                           avci->initial_channels       != frame->channels ||
                           avci->initial_channel_layout != frame->channel_layout;
                break;
            }

            if (changed) {
                avci->changed_frames_dropped++;
                av_log(avctx, AV_LOG_INFO, "dropped changed frame #%d pts %"PRId64
                                            " drop count: %d \n",
                                            avctx->frame_number, frame->pts,
                                            avci->changed_frames_dropped);
                av_frame_unref(frame);
                return AVERROR_INPUT_CHANGED;
            }
        }
    }
    return 0;
}



static int decode_receive_frame_internal(AVCodecContext *avctx, AVFrame *frame)
{
    AVCodecInternal *avci = avctx->internal;
    int ret;

    av_assert0(!frame->buf[0]);

    if (avctx->codec->receive_frame)
    //在这里执行
        ret = avctx->codec->receive_frame(avctx, frame);
    else
        ret = decode_simple_receive_frame(avctx, frame);

    if (ret == AVERROR_EOF)
        avci->draining_done = 1;

    if (!ret) {
        /* the only case where decode data is not set should be decoders
         * that do not call ff_get_buffer() */
        av_assert0((frame->private_ref && frame->private_ref->size == sizeof(FrameDecodeData)) ||
                   !(avctx->codec->capabilities & AV_CODEC_CAP_DR1));

        if (frame->private_ref) {
            FrameDecodeData *fdd = (FrameDecodeData*)frame->private_ref->data;

            if (fdd->post_process) {
                ret = fdd->post_process(avctx, frame);
                if (ret < 0) {
                    av_frame_unref(frame);
                    return ret;
                }
            }
        }
    }

    /* free the per-frame decode data */
    av_buffer_unref(&frame->private_ref);

    return ret;
}