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

Måns Rullgård mru
Mon Jan 30 11:40:12 CET 2006

Michel Bardiaux said:
> M?ns Rullg?rd wrote:
>> Colin Ward <lists at codehq.org> writes:
>>>M?ns Rullg?rd wrote:
>>>>I can think of many reasons to want a proper MPEG file rather than a
>>>>encapsulated one.  The OP's file apparently causes problems for ffmpeg.
>>>>>   I have a VCD related problem that I have been meaning to look into.
>>>>>I have a couple of .dat files from a couple of different VCDs.  One of
>>>>>them plays in my FFMPEG based program and the other causes either
>>>>>av_open_input_file() or av_find_stream_info() to return an "unknown
>>>>>format" error.  I can't remember exactly at the moment as I am not in
>>>>>front of my development computer.
>>>>>   Why would one VCD .dat file be playable and not the other?
>>>>Post some samples, please.
>>>   Sorry for the delay, I haven't been home for a few days to upload
>>>   the samples.  They can be found here:
>>>   http://www.codehq.org/Robots.dat
>>>   http://www.codehq.org/Legue.dat
>>>   They are both the first 1 MB from the respective .dat files on the
>>>   VCD.  As I said, one of them opens successfully and the other
>>>   returns an "unknown format" error.  And yet they both open
>>>   successfully with MPlayer.
>> 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.
> 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?

M?ns Rullg?rd
mru at inprovide.com

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