[Matroska-devel] [Cellar] Channel Positions for Multichannel LPCM Track Inside Matroska
Steve Lhomme via Matroska-devel
matroska-devel at lists.matroska.org
Sun May 8 14:05:30 CEST 2016
2016-04-24 17:39 GMT+02:00 Nithin Mathew Kurien <nithinmkurien at gmail.com>:
> Currently the specification for storing a multichannel LPCM track (CodecID
> A_PCM/INT/LIT) inside a Matroska file [1, 2], does not specify a way to
> indicate the channel positions of the track. Due to this, players find it
> difficult to map the channels to the correct speaker positions when playing
> such a track. MakeMKV employs a workaround for this problem. It stores the
> track under the CodecID A_MS/ACM, along with a WAVEFORMATEXTENSIBLE
> structure in CodecPrivate. This structure contains a field called
> dwChannelMask which specifies the channel positions . This is identical
> to the way LPCM is stored inside AVI files. The problem with this approach
> is that most players do not recognise the CodecID A_MS/ACM, except for a few
> open-source players like Kodi .
We used to have a field for that but it was never used AFAIK
This is how it used to be, describing each speaker position with an
angle. I don't know there is a standard way to express this. I'd
assume the distance to the center should play a role too.
> In the case of a FLAC track (inside either a raw .FLAC file or a .MKA file),
> we can specify an optional WAVEFORMATEXTENSIBLE_CHANNEL_MASK tag . Could
> a similar solution be implemented for LPCM inside Matroska too?
> On a related note, the ffmpeg documentation  specifies additional channel
> positions which are not found in the Microsoft documentation , like Wide
> Left and Wide Right speakers. Are these speaker positions recognised by
> players when reading WAV files?
VLC currently handles 'only' 9 speaker positions out of the 18 MS ones.
>  https://matroska.org/technical/specs/codecid/index.html
>  http://haali.su/mkv/codecs.pdf
>  http://www.makemkv.com/forum2/viewtopic.php?f=8&t=2530
>  https://sourceforge.net/p/mediainfo/discussion/297609/thread/164b4fb3/
>  https://ffmpeg.org/doxygen/2.2/channel__layout_8h_source.html
> Thanks and regards,
> Cellar mailing list
> Cellar at ietf.org
Matroska association Chairman
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