GNOME Bugzilla – Bug 448861
Problems with multichannel AAC -> Vorbis transcoding
Last modified: 2008-06-20 11:07:36 UTC
The file http://images.apple.com/movies/fox/fantastic_4-silver_surfer/fantastic4silversurfer-tlr1_h720p.mov contains, according to Totem, a 7.1-channel AAC track (although VLC says it's 6-channel). Attempting to transcode the audio to Vorbis with the standard pipeline: gst-launch-0.10 filesrc location=1.mov ! decodebin ! queue ! audioconvert ! vorbisenc ! oggmux ! filesink location=2.ogg generates a mono Vorbis stream rather than the multichannel one would expect. Forcing the caps to "audio/x-raw-float, channels=5" (for example) in between audioconvert and vorbisenc will generate a multichannel vorbis file, but the channel mapping seems to be incorrect (centre audio seems to come through the right speaker, for example). I'm not sure whether this is a bug in faad, audioconvert or vorbisenc, so I'm leaving it as "don't know". If you need any more info, please let me know
With the latest fixes to audioconvert in gst-plugins-base this transcoding now produce a 5.1 file correctly. Haven't been able to verify 100% if the channel mapping is correct though, but so far things look ok.
This is fixed in 0.10.20 now by 2008-05-29 Sebastian Dröge <slomo@circular-chaos.org> * ext/vorbis/vorbisdec.c: (vorbis_handle_identification_packet): * ext/vorbis/vorbisenc.c: (gst_vorbis_enc_generate_sink_caps): Add sane defaults for the 7 and 8 channel layouts as those are undefined in the Vorbis spec. Use NONE channel layouts when decoding more than 8 channels instead of erroring out. Fixes bug #535356. The case with the capsfilter should be fixed by one of the audioconvert changes between 0.10.19 and 0.10.20.