Le lun. 10 mars 2025 à 15:46, Michael Niedermayer
<mich...@niedermayer.cc> a écrit :
>
> On Mon, Mar 10, 2025 at 08:50:06AM -0500, Romain Beauxis wrote:
> > Le dim. 9 mars 2025 à 13:31, Michael Niedermayer
> > <mich...@niedermayer.cc> a écrit :
> > >
> > > On Tue, Feb 25, 2025 at 04:01:14PM -0600, Romain Beauxis wrote:
> > > > libavcodec/decode.c: intercept `AV_PKT_DATA_METADATA_UPDATE` packet
> > > > extra data, attach them to the next decoded frame.
> > > >
> > > > ---
> > > > libavcodec/decode.c | 20 ++++++++++++++++++++
> > > > 1 file changed, 20 insertions(+)
> > > >
> > > > diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> > > > index cac7e620d2..96e2f0ce95 100644
> > > > --- a/libavcodec/decode.c
> > > > +++ b/libavcodec/decode.c
> > > > @@ -97,6 +97,8 @@ typedef struct DecodeContext {
> > > > int lcevc_frame;
> > > > int width;
> > > > int height;
> > > > +
> > > > + AVDictionary *pending_metadata;
> > > > } DecodeContext;
> > > >
> > > > static DecodeContext *decode_ctx(AVCodecInternal *avci)
> > > > @@ -729,6 +731,8 @@ int attribute_align_arg
> > > > avcodec_send_packet(AVCodecContext *avctx, const AVPacke
> > > > {
> > > > AVCodecInternal *avci = avctx->internal;
> > > > DecodeContext *dc = decode_ctx(avci);
> > > > + const uint8_t *side_metadata;
> > > > + size_t size;
> > > > int ret;
> > > >
> > > > if (!avcodec_is_open(avctx) || !av_codec_is_decoder(avctx->codec))
> > > > @@ -746,6 +750,14 @@ int attribute_align_arg
> > > > avcodec_send_packet(AVCodecContext *avctx, const AVPacke
> > > > ret = av_packet_ref(avci->buffer_pkt, avpkt);
> > > > if (ret < 0)
> > > > return ret;
> > > > +
> > > > + side_metadata = av_packet_get_side_data(avpkt,
> > > > AV_PKT_DATA_METADATA_UPDATE, &size);
> > > > + if (side_metadata) {
> > > > + av_dict_free(&dc->pending_metadata);
> > > > + ret = av_packet_unpack_dictionary(side_metadata, size,
> > > > &dc->pending_metadata);
> > > > + if (ret < 0)
> > > > + return ret;
> > > > + }
> > > > } else
> > > > dc->draining_started = 1;
> > > >
> > > > @@ -815,6 +827,7 @@ fail:
> > > > int ff_decode_receive_frame(AVCodecContext *avctx, AVFrame *frame)
> > > > {
> > > > AVCodecInternal *avci = avctx->internal;
> > > > + DecodeContext *dc = decode_ctx(avci);
> > > > int ret;
> > > >
> > > > if (!avcodec_is_open(avctx) || !av_codec_is_decoder(avctx->codec))
> > > > @@ -887,6 +900,12 @@ int ff_decode_receive_frame(AVCodecContext *avctx,
> > > > AVFrame *frame)
> > > > }
> > > > }
> > > > #endif
> > > > +
> > > > + if (dc->pending_metadata) {
> > > > + av_dict_copy(&frame->metadata, dc->pending_metadata,
> > > > AV_DICT_APPEND);
> > > > + av_dict_free(&dc->pending_metadata);
> > > > + }
> > > > +
> > > > return 0;
> > > > fail:
> > > > av_frame_unref(frame);
> > >
> > > Does this work correctly, if theres a delay/latency in the decoder ?
> >
> > Can you describe a scenario that you're thinking about?
>
> The users feeds several packets into a multi threaded decoder
> and then depending on the threads and luck sooner or later
> one frame comes out.
>
> Passing some data in a way that disregards this, feels wrong
> Hypothetically there also could be a 2nd AV_PKT_DATA_METADATA_UPDATE
> going in before the frame corresponding to the first comes out
> but i may be missing something
As far as I can tell, the mechanism is only used by ogg streams and
for ogg, these scenarios would not really apply I believe.
Currently, DTS are broken for chained ogg streams so passing packets
in any other order than the stream's sequential order would not work.
I think this concern could be addressed in the planned follow-up work,
which is to remove the ogg headers from the demuxer and attach
AV_PKT_DATA_METADATA_UPDATE to a packet with actual media content.
In this case, the metadata would be immediately attached to the frame
when the packet is decoded.
-- Romain
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