[Ffmpeg-devel] [Ffmpeg-devel-old] SVCD bug (original) (raw)

Justin Ruggles jruggle
Thu Feb 2 03:11:02 CET 2006

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

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