[Matroska-devel] Timestamp precision in matroska files

Jory jcsston at wiesneronline.net
Tue Jan 6 20:04:30 CET 2004


:sigh:
 I've said this many times, the muxer I'm working on will FIX sample accuarte seeking by using the sample rate as the timecode scale.

It's buggy right now and I'm trying to work on it as fast as I can


Later,
Jory
  ----- Original Message ----- 
  From: Christian HJ Wiesner 
  To: Discussion about the current and future development of Matroska 
  Sent: Tuesday, January 06, 2004 11:07 AM
  Subject: [Matroska-devel] Timestamp precision in matroska files



  Hi,

  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 acceptable
   <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.

  Christian



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