=[SPAM?]= Re: [Matroska-devel] Timestamp precision in matroska files

Frank Klemm pfk at fuchs.offl.uni-jena.de
Wed Jan 7 01:57:40 CET 2004


On Tue, Jan 06, 2004 at 08:17:14PM +0100, Steve Lhomme wrote:
> 
> >>
> >> <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
> > 
> > 
> > The scale can be adjusted by will.
> > 
> >>  <ChrisHJW> or is 10 µs ok ?
> >>  <Case> is not for high rates
> > 
> > 
> > Then we need a new block type, with more than 16 bits for the timecode.
> 
> What about the same Block using a new attached (in BlockMore) containing 
> the number of samples since the beggining ? A la Granule Pos.
> This could apply to video for the number of frames too.
> 
> That's backward compatible and add a neat feature.
> 
What about A/V material with changing frame rates (mixed CCIR, FCC/IAC and
cinema material) ???

Current medias are in a format, where the source format is converted to the
frame rate of your region (i.e. 50 or 60 frames per seconds). When the
diplay convert this rate again, it is done twice, not nice for quality.

Also most convertings are really low quality.

Better would be when all material can be mixed in a file, the decoder +
display render engine translates the signal into the needs of the display.

This re-rendering ist done for

- horizontal pixels for displays with a horizontal discrete structure (LCDs, LEDs, DLPs)
- vertical lines for displays with a vertical discrete structure (all
  electronic displays)
- in the time domain (for all displays with flicker reduction and more
  complex computation of intermediate images)

Also note that the interlacing can be changed inside a stream. You can have
a DVD with a non-interlaced movie and the final credits are interlaced.
It is even possible that regions of a single frame are interlaced and other
not!

Audio Time Code:
- Low  Res (normally exact enough for sample exact cuttering): 48000 ticks/sec
- High Res (enough for nearly all):                           192000 ticks/sec

Video Time Code:
- Low  Res (normally exact enough for sample exact cuttering):   300 ticks/sec
- High Res (enough for nearly all):                             1200 ticks/sec

Combined Audio/Video Time Code:
- Low  Res (normally exact enough for sample exact cuttering): 48000 ticks/sec
- High Res (enough for nearly all):                           192000 ticks/sec


Note: 

- You also must define exact rounding rules for sample precise cuttering
  (otherwise you have problems even with 192 kHz Time Code when using audio
  with 44100 Hz).

- It should be defined how to handle FCC/IAC "nice" rate of 
  59.94005232862375719518... Hz

  a) exact 60 Hz, don't care about the 0.1% error (which was intended to
     reduce interference between color and audio carrier in radio transmissions)
  b) 59.94 Hz (ca. 0,9 ppm error)
  c) 2863636 / 47775 Hz (exact theoretical value)

-- 
Frank Klemm



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