[mythtv] Requantisation for DVD creation in MythArchive

[John Pilkington]

In January I reported that using tcrequant to shrink recordings to fit 
onto a DVD caused picture corruption in fc10 but not in CentOS_5.  At 
about the same time tcrequant was deprecated and is no longer built by 
default in the transcode releases.

In a reply on mythdev, vamps was suggested as a possible alternative, 
and I have been looking into this with some, but not enough, success.

Both tcrequant and vamps use requantiser code released by MetaKine;
vamps uses a later rewrite in a wrapper, and is supposed to be able to 
shrink DVD-compliant mpeg2 files for input to dvdauthor.

In my experience this can work well, but there are problems at the 
end-of-file.  dvdauthor expects files created by mplex -f 8, but vamps 
unmodified treats the end-marker in the final 2kb block as an error and 
does an immediate exit without writing its buffer.  If modified to 
ignore the end marker it does not create one in its output.

I have tried truncating the vamps output and appending an end marker 
copied from the input file.  dvdauthor will often accept this, but for 
some files it is unable to process the final VOBU of a recording, and 
aborts.

It looks as if vamps might be usable if its output files could be 
truncated and re-tailed at the last valid nav packet.  It might be 
possible to do this within vamps or mythburn.py, or it might be possible 
to modify the input files left in the working directory after dvdauthor 
has failed.  At present I have not worked out a way to do any of these.

vamps functionality is not, afaik, maintained now.  I don't think I 
could hack mplex or dvdauthor.

John P