| Message ID | 20220908113632.1056-2-jyrkive@nekonyansoft.com |
|---|---|
| State | Accepted |
| Commit | 8fc2dedfe6e8fcc58dd052bf3b85cd4754133b17 |
| Headers | show |
| Series | [FFmpeg-devel] avcodec: Vorbis decode: don't use a flag to determine if frames have been output | expand |
| Context | Check | Description |
|---|---|---|
| andriy/commit_msg_x86 | warning | Please wrap lines in the body of the commit message between 60 and 72 characters. |
| andriy/make_x86 | success | Make finished |
| andriy/make_fate_x86 | success | Make fate finished |
On 9/8/22, jyrkive@nekonyansoft.com <jyrkive@nekonyansoft.com> wrote: > From: Jyrki Vesterinen <jyrkive@nekonyansoft.com> > > If a developer using FFmpeg libraries seeks into an earlier position and > calls > avcodec_flush_buffers() afterwards as recommended, the Vorbis decoder will > drop > the next frame, since buffer flushing clears the first_frame flag. As a > result, > the audio samples the calling code receives may be ahead of the requested > seek > position, which is unacceptable in some use cases such as playing a looping > sound effect. > > This commit records the presentation timestamp of the first frame and > determines after that if the new frame is the first frame (possible after > seeking to the start) by comparing its pts to the stored pts. > --- > libavcodec/vorbisdec.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c > index 4d03947c49..38a5367be3 100644 > --- a/libavcodec/vorbisdec.c > +++ b/libavcodec/vorbisdec.c > @@ -131,6 +131,7 @@ typedef struct vorbis_context_s { > > FFTContext mdct[2]; > uint8_t first_frame; > + int64_t initial_pts; > uint32_t version; > uint8_t audio_channels; > uint32_t audio_samplerate; > @@ -1847,6 +1848,10 @@ static int vorbis_decode_frame(AVCodecContext *avctx, > AVFrame *frame, > > if (!vc->first_frame) { > vc->first_frame = 1; > + vc->initial_pts = frame->pts; > + } > + > + if (frame->pts == vc->initial_pts) { > *got_frame_ptr = 0; > av_frame_unref(frame); > return buf_size; > @@ -1881,7 +1886,6 @@ static av_cold void vorbis_decode_flush(AVCodecContext > *avctx) > sizeof(*vc->saved)); > } > vc->previous_window = -1; > - vc->first_frame = 0; > } > > const FFCodec ff_vorbis_decoder = { > -- > 2.37.2.windows.2 > LGTM > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe". >
diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c index 4d03947c49..38a5367be3 100644 --- a/libavcodec/vorbisdec.c +++ b/libavcodec/vorbisdec.c @@ -131,6 +131,7 @@ typedef struct vorbis_context_s { FFTContext mdct[2]; uint8_t first_frame; + int64_t initial_pts; uint32_t version; uint8_t audio_channels; uint32_t audio_samplerate; @@ -1847,6 +1848,10 @@ static int vorbis_decode_frame(AVCodecContext *avctx, AVFrame *frame, if (!vc->first_frame) { vc->first_frame = 1; + vc->initial_pts = frame->pts; + } + + if (frame->pts == vc->initial_pts) { *got_frame_ptr = 0; av_frame_unref(frame); return buf_size; @@ -1881,7 +1886,6 @@ static av_cold void vorbis_decode_flush(AVCodecContext *avctx) sizeof(*vc->saved)); } vc->previous_window = -1; - vc->first_frame = 0; } const FFCodec ff_vorbis_decoder = {
From: Jyrki Vesterinen <jyrkive@nekonyansoft.com> If a developer using FFmpeg libraries seeks into an earlier position and calls avcodec_flush_buffers() afterwards as recommended, the Vorbis decoder will drop the next frame, since buffer flushing clears the first_frame flag. As a result, the audio samples the calling code receives may be ahead of the requested seek position, which is unacceptable in some use cases such as playing a looping sound effect. This commit records the presentation timestamp of the first frame and determines after that if the new frame is the first frame (possible after seeking to the start) by comparing its pts to the stored pts. --- libavcodec/vorbisdec.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)