[Matroska-devel] Matroska-devel Digest, Vol 110, Issue 1

madshi madshi at gmail.com
Thu Jun 7 12:16:12 CEST 2012

> Date: Thu, 7 Jun 2012 09:17:00 +0200
> From: Moritz Bunkus <moritz at bunkus.org>
> due to a recent bug report for mkvmerge I stumbled across this...
> undefined part in our specs. DTS-MA (Master Audio) can actually
> have two different number of encoded channels.

That's not really new. Even standard DTS supports extensions. You can have
a 5.1 standard DTS file with an XCh or XXCh extension, increasing the
channel count to 6.1 or 7.1. Or you could have an X96 extension to increase
sampling rate from 48khz to 96khz. Or you could even have both XCh and X96
extensions. Some DTS decoders are able to decode those extensions, some are
not. This is all still standard DTS, with no DTS-HD involved.

DTS-HD is just more of the same. DTS-HD introduces more extensions and a
totally new bitstream element, so there are even more variations. But it's
still the same principle as with standard DTS. I'm not 100% sure but it's
probably even possible to have a DTS-HD track with 3 possible channel
counts. E.g. you could have 6.1 core, with an XLL (= DTS-MA) extension to
7.1. So basically the core without the XCh extension is 5.1, the core with
the XCh extension is 6.1 and with the DTS-HD XLL extension it's 7.1. I'm
not sure if this is ever used in real life, but it's probably possible.

There's a similar problem with E-AC3 and TrueHD, too, btw. Some decoders
are able to decode full 7.1. Some decoders are only able to decode 5.1.

I think the best solution would be to store the max capability of the track
into the MKV headers. If some decoders are not able to decode the full
information then that's their problem and not the problem of the MKV file.

Just my 2 cents, though...

Best regards, Mathias.
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