Hi Bob,
> > 1. There is a bug in mplex' look-up table that gives the length of AC3
> > frames from the encoded frame-length.
>
> Ummm...Not likely, right?
Actually, I just heard from Steven that he may have encountered the issue
himself. Could be a bug in the AC3 reading code that (e.g.) does bad things
if bit-rate changes in mid-stream or something like that.
> > 2. The AC3 stream is corrupt.
>
> Could be, I guess. More below.
>
> > Mplex reckons it at byte 349129984 in the AC3 stream. Now 448 kbit/sec
> > corresponds to a mere 56000 bytes per second. So mplex reckons it is 103
> > minutes into the audio stream. If this is very near or at the end of
> > the video stream the probable cause is simple: something upstream
> > truncated / corrupted the last AC3 frame. Simply chopping of 1-2KB from
> > the end of the stream should solve your problem (mplex can recover from
> > the last frame being chopped off).
>
> Woooo... OK, I think I know what you are saying. But certainly don't know
> what to do about that. How does one "chop off" a couple of kb?
Unix/linux has a nice collection of general-purpose file-processing tools.
There's one called 'head' that allows you to copy the first so-and-so many
bytes of file.
head --bytes=<point I want to chop file off> at original_file >
chopped_version
In your case:
head --bytes=349129984 orginal.ac3 > chopped.ac3
There is of course a corresponding 'tail' that allows you to copy the bytes
after byte so-and-so or the last so-and-so bytes of a file.
Combine with 'cat' (which outputs the result of chaining together various
files) and a little imagination and lots of useful things can be done.
> > Other things to try:
> >
> > - Try re-extracting the AC3.
>
> Did that twice, with two different DVDs. same result
Hmmm... that makes a systematic error either in the extraction or in mplex
parsing software 99.9% likely to be the problem. Can you run a few quick
tests for me to see if we can isolate the problem?
I need to know how long the original AC3 file was...
What happens if you mplex with the a some AC3 taken off the front of the
sequence
run
tail --bytes=+179200 your_original.ac3 > shifted.ac3
and then 'mplex' with 'shifted.ac3' instead of your original .ac3 file.
If you've got the disk-space spare pls. don't discard the .ac3 - if it looks
like an mplex problem it would be super-useful to be able to email me the
critical section where things go wrong to debug mplex.
cheers,
Andrew
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