[FFmpeg-devel] [PATCH v2 1/3] libavformat/oggparseflac.c: Decode metadata packets.

[toots at rastageeks.org]

From: Romain Beauxis <toots at rastageeks.org>

This is the second version of a patch to add support for in-stream metadata
updates in the ogg/flac parser.

Currently, FFmpeg is unable to decode metadata in chained ogg/flac bitstreams
past the initial track. This impacts all users relying on the FFmpeg backend to
decode chained ogg/flac streams.

Documentation on ogg chained bitstreams can be found here: https://xiph.org/ogg/doc/oggstream.html

Code for detecting metadata frame is based on libavcodec/flacdec.c, code for
handling comment update is based on libavformat/oggparsevorbis.c.

This fix has been successfully tested locally. To reproduce:
* Find a ogg/flac icecast stream, for instance from: https://dir.xiph.org/
* Decode the stream using FFMpeg API
* Check the associated AVStream metadata

I have not been able to find a reproduction test with the ffmpeg or ffplay
CLI. However, the patch is confirmed to fix the backend from liquidsoplaySee:
https://github.com/savonet/liquidsoap/issues/3010

I would be happy to provide more details or even a reproduction minimal example
using the C API.

---
 libavformat/oggparseflac.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/libavformat/oggparseflac.c b/libavformat/oggparseflac.c
index eef6e09927..1dd292483d 100644
--- a/libavformat/oggparseflac.c
+++ b/libavformat/oggparseflac.c
@@ -126,10 +126,30 @@ fail:
     return ret;
 }
 
+static int flac_packet(AVFormatContext *s, int idx)
+{
+    struct ogg *ogg = s->priv_data;
+    struct ogg_stream *os = ogg->streams + idx;
+    int ret;
+
+    if (os->psize > 4 && (*(os->buf + os->pstart) & 0x7F) == FLAC_METADATA_TYPE_VORBIS_COMMENT) {
+        AVStream *st = s->streams[idx];
+        av_dict_free(&st->metadata);
+        ret = ff_vorbis_stream_comment(s, st, os->buf + os->pstart + 4,
+                                       os->psize - 4);
+
+        if (ret < 0) return ret;
+    }
+
+    return 0;
+}
+
+
 const struct ogg_codec ff_flac_codec = {
     .magic = "\177FLAC",
     .magicsize = 5,
     .header = flac_header,
+    .packet = flac_packet,
     .nb_header = 2,
 };
 
-- 
2.37.1 (Apple Git-137.1)