[Matroska-devel] Timestamp precision in matroska files

Christian HJ Wiesner chris at matroska.org
Tue Jan 6 18:07:45 CET 2004


here an interesting log from #foobar2000 :
<ChrisHJW> DEATH : are you here ?
 <DEATH> yes
 <ChrisHJW> DEATH : there is an alpha muxer to write MKA files with 
factor 10 higher time resolution
 <ChrisHJW> 100 µs
 <Case> not enough
 <DEATH> ^^
 <ChrisHJW> would this help ?
 <Case> it would not
 <DEATH> still inaccurate
 <ChrisHJW> what resolution would you need ?
 <DEATH> and i havent tried jcsston's new muxer, blah
 <DEATH> gonna do it now
 <DEATH> needs to be greater than samplerate
 <DEATH> or equal to samplerate
 <Case> samplerate or way higher
 <DEATH> more like what Case said
 <DEATH> must be enough to point any sample with time values
 <ChrisHJW> 1 / 44100 = 22 µs ?
 <ChrisHJW> 1 / 48000 = 20 µs ?
 <ChrisHJW> Hmm .... so even 10 µs would help much, right ? you need 1 µs ?
 <ChrisHJW> wouldnt
 <ChrisHJW> or is 10 µs ok ?
 <Case> is not for high rates
 <DEATH> 10 looks like it could be enough
 <DEATH> for 48000hz that is
 <DEATH> how about just making it equal to samplerate ?
 <ChrisHJW> Case : 96 KHz is quite unlikely to be lossy compressed ?
 <Case> no it isn't
 <ssamadhi97> think dvd audio
 <Case> perfect for lossy compression, no one will miss > 22kHz
 <ChrisHJW> ssamadhi97 : if its PCM 96 Khz, it wont be a problem
 <ChrisHJW> matroska container can have a resolution of 1 ns
 <ChrisHJW> BUT
 <ChrisHJW> the maximum length for a cluster is then limited
 <ChrisHJW> and this will have huge impact on overhead, especially for 
low bitrate lossy compression
 *<DEATH> how is that mp4 doesnt have this issue ? :B*
 <ChrisHJW> for high bitrate lossless or PCM, the overhead would be 
 <DEATH> lets see.. because it stores only frame durations and 
compresses them because they are repetitive ?
 <menno> RLE ist god
 <DEATH> ^_^
 <DEATH> would probably puke on vorbis
 <DEATH> then again, noone wants vorbis in mp4
 <menno> then again, noone wants vorbis
 <DEATH> that too
 <Case> ChrisHJW: that inaccuracy in matroska must cause sync problems 
with video and audio
 <Case> and make inaccurate video seeking also impossible
 <DEATH> not with +-1ms inaccuracy
 <DEATH> i wonder what kind of sound lag console/whatever emulators have
 <ChrisHJW> Case : you wont notice a lag between video and audio of 1 ms
 <Case> that's still unacceptable
 <DEATH> Case: emulators probably have 30ms+ sound lag, and people still 
dont notice that
 <ChrisHJW> even 100 ms are hard to distinguish
 <DEATH> until i tried to play vagrant story on ePSXe after playing it 
to death on real console
 <DEATH> all my chained attacks were screwed
 <DEATH> because they relied on sound
 <ChrisHJW> you see there is something wrong, but you cant say if its 
too early or too late
 <ssamadhi97> haha
 *<Case> I remember how matroska was advertised as great for video 
editing because of accurate seeking and such. if it isn't accurate and 
time codes people see are pulled from ass it's unusable*

Any comments on this ? I dont have enough knowledge about why it was 
designed this way to reply accordingly.

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