[vlc-devel] Coping with faulty MPEG streams and SVCD subtitles

[R. Bernstein]

I'd like to add a hack to vlc's system.c to make it more tolerant of
the kind of bug in MPEG streams that WinSubMux produces. This should
help moving SVCD subtitle support forward.

The current situtation: vlc's MPEG demuxer does not tolerate the
faulty kind of MPEG stream produced by the SVCD and CVD subtitling
program WinSubMux. Apparently WinSubMux does not renumber the pack
headers of a MPEG when it multiplexes subtitles in. Although this
program appears to be used quite a bit, it is not open source, and the
author is somewhat anonymous. I've sent a bug report to the contact
listed for the program, but I doubt if this long-outstanding bug will
be fixed in the predictable future.

One reason WinSubMux is popular and is likely to remain so is because
there really aren't free tools for SVCD, and CVD authoring. This is I
think the only one. Even comercial subtitle creation programs are
rare, and all run only under Microsoft Operating Systems. So I see the
situtation as a chicken-and-egg problem. Few media players currently
support subtitles, and this doesn't encourage developing open-source
subtitle authoring tools on non-Microsoft operating systems.

As a proof of concept, I patched my copy of system.c so that the SCR
is delayed by one PACK value and if we see a private stream, this
signals ignoring the current PACK header SCR. 

Unless there are objections, I'll clean up the code a little and
commit it.

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