[Matroska-devel] CodecSpecs

Moritz Bunkus moritz at bunkus.org
Mon Jan 10 09:22:47 CET 2011


Hey,

On Monday 10 January 2011 02:24:08 Santiago Jimeno wrote:

> Regarding MLP-TrueHD, I made what you tell me in your e-mail, but without
> success.
> MLP contain in the blocks the whole header beginning with F8726FBB, but
> TrueHd doesn't contain the first 4 bytes of the header (F8726FBA).

My guess is that you don't take header removal compression into account
http://www.bunkus.org/videotools/mkvtoolnix/faq.html#header_removal_compression

The code in mkvmerge is the same for MLP and TrueHD. In fact, it's the
same source file with very few conditional code for distinction between
MLP/TrueHD.

> The samples that I am using are:
> http://samples.mplayerhq.hu/A-codecs/TrueHD/TrueHD%20Sample%201%20(Final%20
> Fantasy%20VII%20Advent%20Children).mkv
> http://samples.mplayerhq.hu/A-codecs/TrueHD/TrueHD%20Sample%202%20(Evangel
> ion%201.11%20You%20Are%20(Not)%20Alone).mkv

Ok those do not use header removal compression. Interesting. Let's see:

[0 mbunkus at ls-bs-ws4 ~/dl] mkvinfo -v -v TrueHD\ Sample\ 1\ \(Final\ Fantasy\ 
VII\ Advent\ Children\).mkv| grep 'track number 2' | head -n 1
| + SimpleBlock (track number 2, 1 frame(s), timecode 0.000s = 00:00:00.000) 
at 154845

So the very first audio track's frame starts at position 154845 in the
file. Using a hex editor the bytes are really not the sync word. This
could be a bug in mkvmerge. I'll try to investigate this sometime this
week.

> I have observed that you with Mkvtool can calculate the duration of
> MLP-TrueHd audio file to make the MKA file.
> It has been impossible for my to calculate the duration with the data
> provided by the original audio file.
> Would you be able to help me in this?

I don't have time to explain (I'm at work), but all the relevant code is
in these two files:

http://www.bunkus.org/cgi-
bin/gitweb.cgi?p=mkvtoolnix.git;a=blob;f=src/output/p_truehd.cpp;h=7562d0604c9103ec37d18300f76a925a8d11a737;hb=HEAD
http://www.bunkus.org/cgi-
bin/gitweb.cgi?p=mkvtoolnix.git;a=blob;f=src/common/truehd.cpp;h=aad48c34055b5cfbd5bdae2ce8f76b7311bc98c3;hb=HEAD

Regards,
Mosu
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