ffmpeg 源代码简单学习 ： avcodec_decode_video2()
参考博客：https://blog.csdn.net/leixiaohua1020/article/details/12679719
int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *picture,
int *got_picture_ptr,
const AVPacket *avpkt)
{
//调用compat_decode函数
return compat_decode(avctx, picture, got_picture_ptr, avpkt);
}
//===============================================
static int compat_decode(AVCodecContext *avctx, AVFrame *frame,
int *got_frame, const AVPacket *pkt)
{
AVCodecInternal *avci = avctx->internal;
int ret = 0;
av_assert0(avci->compat_decode_consumed == 0);
if (avci->draining_done && pkt && pkt->size != 0) {
av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
avcodec_flush_buffers(avctx);
}
*got_frame = 0;
if (avci->compat_decode_partial_size > 0 &&
avci->compat_decode_partial_size != pkt->size) {
av_log(avctx, AV_LOG_ERROR,
"Got unexpected packet size after a partial decode\n");
ret = AVERROR(EINVAL);
goto finish;
}
//调用函数 avcodec_send_packet函数
if (!avci->compat_decode_partial_size) {
ret = avcodec_send_packet(avctx, pkt);
if (ret == AVERROR_EOF)
ret = 0;
else if (ret == AVERROR(EAGAIN)) {
/* we fully drain all the output in each decode call, so this should not
* ever happen */
ret = AVERROR_BUG;
goto finish;
} else if (ret < 0)
goto finish;
}
while (ret >= 0) {
//循环调用avcodec_receive_frame函数
ret = avcodec_receive_frame(avctx, frame);
if (ret < 0) {
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
ret = 0;
goto finish;
}
if (frame != avci->compat_decode_frame) {
if (!avctx->refcounted_frames) {
ret = unrefcount_frame(avci, frame);
if (ret < 0)
goto finish;
}
*got_frame = 1;
frame = avci->compat_decode_frame;
} else {
if (!avci->compat_decode_warned) {
av_log(avctx, AV_LOG_WARNING, "The deprecated avcodec_decode_* "
"API cannot return all the frames for this decoder. "
"Some frames will be dropped. Update your code to the "
"new decoding API to fix this.\n");
avci->compat_decode_warned = 1;
}
}
if (avci->draining || (!avctx->codec->bsfs && avci->compat_decode_consumed < pkt->size))
break;
}
finish:
if (ret == 0) {
/* if there are any bsfs then assume full packet is always consumed */
if (avctx->codec->bsfs)
ret = pkt->size;
else
ret = FFMIN(avci->compat_decode_consumed, pkt->size);
}
avci->compat_decode_consumed = 0;
avci->compat_decode_partial_size = (ret >= 0) ? pkt->size - ret : 0;
return ret;
}
//===========================================================
int attribute_align_arg avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt)
{
AVCodecInternal *avci = avctx->internal;
int ret;
if (!avcodec_is_open(avctx) || !av_codec_is_decoder(avctx->codec))
return AVERROR(EINVAL);
if (avctx->internal->draining)
return AVERROR_EOF;
if (avpkt && !avpkt->size && avpkt->data)
return AVERROR(EINVAL);
av_packet_unref(avci->buffer_pkt);
if (avpkt && (avpkt->data || avpkt->side_data_elems)) {
ret = av_packet_ref(avci->buffer_pkt, avpkt);
if (ret < 0)
return ret;
}
ret = av_bsf_send_packet(avci->bsf, avci->buffer_pkt);
if (ret < 0) {
av_packet_unref(avci->buffer_pkt);
return ret;
}
if (!avci->buffer_frame->buf[0]) {
ret = decode_receive_frame_internal(avctx, avci->buffer_frame);
if (ret < 0 && ret != AVERROR(EAGAIN) && ret != AVERROR_EOF)
return ret;
}
return 0;
}
//============================================================
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 {
ret = decode_receive_frame_internal(avctx, frame);
if (ret < 0)
return ret;
}
//检查视频类型
if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
ret = apply_cropping(avctx, frame);
if (ret < 0) {
av_frame_unref(frame);
return ret;
}
}
//帧数++
avctx->frame_number++;
if (avctx->flags & AV_CODEC_FLAG_DROPCHANGED) {
//如果number=1
if (avctx->frame_number == 1) {
avci->initial_format = frame->format;
switch(avctx->codec_type) {
//编码类型为视频，初始化宽和高
case AVMEDIA_TYPE_VIDEO:
avci->initial_width = frame->width;
avci->initial_height = frame->height;
break;
//编码类型为音频，初始化采样率、声道、 "声道布局??"
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;
}
}
//如果number > 1，则
if (avctx->frame_number > 1) {
//初始化格式
changed = avci->initial_format != frame->format;
switch(avctx->codec_type) {
case AVMEDIA_TYPE_VIDEO://视频类型
changed |= avci->initial_width != frame->width ||
avci->initial_height != frame->height;
break;
case AVMEDIA_TYPE_AUDIO://音频类型
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) {//变化？丢弃
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) {
ret = avctx->codec->receive_frame(avctx, frame);
if (ret != AVERROR(EAGAIN))
av_packet_unref(avci->last_pkt_props);
} else
ret = decode_simple_receive_frame(avctx, frame);
if (ret == AVERROR_EOF)
avci->draining_done = 1;
if (!ret) {
frame->best_effort_timestamp = guess_correct_pts(avctx,
frame->pts,
frame->pkt_dts);
/* 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;
}
