[Matroska-users] mkvtoolnix 1.0 plan: About 64bit

Liisachan Liisachan at faireal.net
Thu Aug 5 04:53:26 CEST 2004


Moritz Bunkus <moritz at bunkus.org> wrote:

> Before I release 0.9.5 we have to make sure that some other apps are
> fixed because mkvtoolnix now uses 64bit floats in Matroska files, and at
> least two authors have only implemented 32bit floats in their
> applications. mkvtoolnix does not violate the Matroska specs in any
> way. 64bit floats is just a feature those two persons haven't
> implemented yet - probably because until now no application was using
> those.

Correct me if I am wrong:

I tested Ogg Vorbis -> MKA, to see if 64-bit will give me better 
precision in duration. But the result was what was quite 
unexpected for me:

Original .ogg
9873696 samples @ 44100Hz
223.89333333333333333 sec
...
.mka by mkvtoolnix 0.9.4
9874387 samples @ 44100Hz 223.90900226757369614 sec
 Duration: 223.909s (00:03:43.909000000)
...
.mka by mkvtoolnix 0.9.4+(64bit)
9874432 samples @ 44100Hz 223.91002267573696145 sec
 Duration: 223.910s (00:03:43.910012712)
...

As you can see, the original is 3:43.893,
but mkvtoolnix-32bit changes .893 into .909
mkvtoolnix-64bit changes .893 into .910

32-bit and 64-bit is about the same (both is not very precise),
and oddly enough, 32-bit is slightly less inaccurate

Then I used mkvextract to re-get Ogg Vorbis, and the result was:
223.907981 (32-bit ver) or 
223.908979 (64-bit ver) while the original is
223.893333

The round trip is lossy.

Tentative Conclusions are,
(1) No difference between 32-bit precision and 64-bit precision 
at least in this test

(2) 64-bit would mean, 
.00000000000000001
in this time scale, but actually, the general precision of the 
Matroska system is like,
.001
or
.01
sec.
If so, is 64-bit really needed?

(3) mkvmerge is "lossy" in duration info, and the error is like 
0.01 sec. So, in theory, if you concatenate 100 MKA files, say, 
in audio editing, then the result could have as much error as 1 
whole sec. What if you muxed such .mka and video in .avi?
1.0 sec out of sync, would be very embarrassing.

*

Just one small test and probably Im misunderstanding something,
but anyway those are what I got using mkvmerge, mkvinfo, 
mkvextract and foobar2000, just so that you know........

Regards

Liisachan





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