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

[Justin Ruggles]

Colin Ward wrote:
> 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?
> 
> 
>>>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.
> 
>    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?
> 

It has been a while since I've messed with VCD, but if I remember
correctly, the leading zeros might have something to do with the
2-second lead-in gap on the VCD track.  I think it depends on how the
*.dat file was extracted from the VCD.

You might want to take a look at
http://savannah.gnu.org/projects/vcdimager/

-Justin