Le lun. 17 févr. 2025 à 10:19, Romain Beauxis <romain.beau...@gmail.com> a écrit : > > This is a series of patches to allow proper decoding of ogg metadata in > chained > `ogg/flac` and `ogg/opus` streams.
I forgot to add: this patch set is also available for review at: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/6 > ## Changes since last version: > - Opus processing moved back to `opus_header` to make sure that opus > demuxing is not impacted by those changes. > - Generic decoding method implemented directly in `libavcodec/decode.c` to > avoid > having each decoded handle the metadata injection. > > ### Summary of code changes: > > The changes in this patch series allow proper decoding of metadata associated > with subsequent streams in chained ogg/flac and ogg/opus bitstream. > > This is done by intercepting ogg packets with comments in the ogg demuxer, > parsing the comment block and attaching it as packed > `AV_PKT_DATA_METADATA_UPDATE` side-data. > > The new metadata can then be unpacked in `libavcodec/decode.c` and attached to > the next decoded frame. > > It is worth noting that is using a mechanism specific to ogg stream that > seemed > to only have been used for vorbis streams so far. > > Along with the changes are new FATE tests validating the implementation. > > ### Discussion and context: > > `ogg/opus` is a pretty popular combination of codec and encapsulation. In > particular, it is widely used in Icecast streams, where chained streams are > the > norm because of the ogg specs requirement for inserting in-band metadata. > > `ogg/flac` streams are pretty important because there are perhaps the only > combination of lossless audio codec and open-source container that allows for > proper transmittion of lossless audio data accross systems such as Icecast, > browser media tags and more. > > In the context of long-running audio streams, the ogg bitstream specs[1] have > historically been very badly implemented. For each new track and each new > metadata, the specs require the logical bitstream to come to a full `EOF` and > then start with a full new logical stream. > > These specs have often been confused with a gobal EOF by most implementations. > > Furtunately, FFmpeg is a little better at that in that it is able to parse > chained logical ogg bitstreams and properly output either encoded ogg packets > or > decoded audio. > > Current limitations with chained ogg streams in FFmpeg include: > 1. Metadata from secondary chained `ogg/flac` and `ogg/opus` bitstreams are > ignored by the demuxer/decoder. > 2. Secondary chained streams packet headers are silently removed by the > demuxer when decoding ogg/opus streams. > 3. No adjustment underlying PTS or DTS: PTS and DTS of secondary chained > streams reset from their own logical stream initia value causing timestamp > discontinuity. > 4. Chained bitstreams with more than one underlying type of content > (audio+video, etc) is not yet supported though this is a much less needed > feature. > > The changes in this patch series address issue #1. > > Future work could address the remaining issues. > -- Romain > > [1]: https://xiph.org/ogg/doc/framing.html > > Romain Beauxis (6): > libavcodec/decode.c: intercept `AV_PKT_DATA_METADATA_UPDATE` packet > extra data, attach them to the next decoded frame. > tests: Add stream dump test API util. > libavformat/oggparseflac.c: Parse ogg/flac comments in new ogg > packets, add them to ogg stream new_metadata. > tests: Add chained ogg/flac stream dump test. > libavformat/oggparseopus.c: Parse comments from secondary chained > streams header packet. > tests: Add chained ogg/opus stream dump test. > > libavcodec/decode.c | 20 +++ > libavformat/oggparseflac.c | 28 +++++ > libavformat/oggparseopus.c | 21 +++- > tests/Makefile | 3 + > tests/api/Makefile | 2 +- > tests/api/api-dump-stream-meta-test.c | 169 ++++++++++++++++++++++++++ > tests/fate/ogg-flac.mak | 11 ++ > tests/fate/ogg-opus.mak | 11 ++ > 8 files changed, 263 insertions(+), 2 deletions(-) > create mode 100644 tests/api/api-dump-stream-meta-test.c > create mode 100644 tests/fate/ogg-flac.mak > create mode 100644 tests/fate/ogg-opus.mak > > -- > 2.39.5 (Apple Git-154) > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
