[VCDImager] Issues with multiplexing system streams

[Paul R. Bernard]

Strictly speaking I doubt that the issues I'm having are caused by
VCDImager, it's most likely the preceding multiplexing step. I'm
attempting to make VCDs from first principles.  ie using only programs
for which I have the source.

I obtained a claimed VCD compliant mpeg system stream (I don't know
how it was made) and burned it onto a CDR with cdrdao from an image
made by VCDImager with no problems.  In particular, VCDImager does not
complain about any 2324 byte block boundary problems.

This CDR plays properly on my DVD player as it does on many others
that have been tested.

I then wanted to make sure I could make system streams so I
demultiplexed it with bbdemux found in bbtools.  Both the video stream
and the audio stream play properly on a computer and pass simple
tests.

I then attempted to multiplex these two streams back into a system
stream.  I've found two multiplexers.  One's call mplex-1.1 by
Christoph Moar, and the other called vcdmplex is buried in VCD-Tools
0.4 by Rainer Johanni.  All streams that I've made with both of these
tools work just fine on a computer (using either a 2048 byte block for
mplex-1.1 or a 2324 byte block.  vcdmplex is fixed at 2324 byte
blocks).

And indeed the system stream made with vcdmplex when burned onto a CDR
(after fixing a padding problem with vcdpad.  I've not looked into
this problem yet.) plays just fine on all tested DVD players.  So to
be accurate I don't actually have a problem.

However it bothers me that I can't figure out why none of the system
streams I've attempted to make with mplex-1.1 and a 2324 byte blocks
play properly on DVD players.  The video seems to be working fine, and
the audio/video sync is fine, but the audio itself is not streaming
smoothly.  It sounds a bit like very brief buffer underruns.  The
pops/clicks/dropouts are happening at approximately 7 Hz and there are
short discordant tones that sound very much like bit streams with
errors that are fed into either a GSM or LPC10 audio codec.

I've fiddled quite of few of the parameters available in mplex,
particularly buffer lengths and buffer delays, but nothing seems to
have any useful effect.  It's got to be either a bug in mplex or
operator error, if indeed it works at all for anything other than a
computer.

I'd very much like to know why this is happening.  Is there anyone
here who can give me a hint?  Are there other multiplexers that I
should be using?

Thanks

- paul