[Ffmpeg-devel] [Ffmpeg-devel-old] SVCD bug

[Måns Rullgård]

Colin Ward said:
> M?ns Rullg?rd wrote:
>  >
>
>    [Snip]
>
>>>> Those files are both unmunged MPEG1 system streams, except for one
>>>> thing.  The one that fails (Legue.dat) starts with a block of 0x11058
>>>> zeros.  That is more junk than lavf searches when checking the file
>>>> format.
>
>    So by "unmunged" I assume that you mean standard MPEG1 files, rather
> than files converted to the VCD format?

Exactly.

>>> Stricto sensu, a bug, since the standard does not place any restriction
>>> on the amount of zero-stuffing.
>>
>> I know, but how far is it reasonable to search for a start code?  Lavf
>> passes the first 2048 bytes of the file to each demuxer when checking the
>> file format.
>>
>> What's the purpose of those leading zeros anyway?
>
>    Who knows!  But they are certainly annoying.  The one thing that I
> know is that no matter what VCD I try they almost all contain these
> "unmunged" MPEG1 files with huge arrays of empty zeros at the start!  In
> other words, very few VCDs work with my media player.

A simple solution might be to attempt reading any file starting with lots of
zeros as MPEG.  I don't know of any other format that allows this.

>    I need to learn a bit more about MPEG 1/2/4, VCDs and DVDs.  Any
> suggestions of a good book that covers these on a file format level?

MPEG1: ISO 11172-1 system, -2 video, -3 audio
MPEG2: ISO 13818-1 PS/TS, -2 video, -3 audio, -7 AAC
MPEG4: ISO 14496-1 QT-like format, -2 video, -3 ACC, -10 AVC, -14 more format
       stuff, save your sanity and leave this to Mike
VCD: White Book, apparently MPEG with some added junk
SVCD: no official standard, MPEG2 video, presumably with added junk
DVD: the spec is yours for $5000, some useful information at
     http://dvd.sourceforge.net/dvdinfo/

-- 
M?ns Rullg?rd
mru at inprovide.com