[FFmpeg-devel] Irregular codec

Jesse L. Zamora xtremek2008
Mon Jun 30 19:21:26 CEST 2008

Kostya wrote:
> On Mon, Jun 30, 2008 at 06:44:55AM -0400, Jesse L. Zamora wrote:
>> Benjamin Larsson wrote:
>>> On Fri, Jun 27, 2008 at 07:58:11PM -0400, Jesse L. Zamora wrote:
>>>> Hello All,
>>>> I've been writing a demuxer and a decoder for the SMV format (SigmaTel 
>>>> Motion Video) for ffmpeg. It begins with a WAV file, then the SMV header 
>>>> afterwards, then an array of jpegs. I was trying to get my demuxer to be 
>>>> able to read the SMV header, but since it's practically in the middle of 
>>>> the file, the buffer is not that big! So I can't read the header through 
>>>> the buffer. How can I somehow read in the middle of the file with the 
>>>> demuxer_probe(AVProbeData *p) function to be able to read the header 
>>>> (especially with demuxer_read_header())?
>>>> Thanks
>>>> Xtreme Kommander
>>> Hi, can you derive that it is a SMV file from the wav header ?
>>> MvH
>>> Benjamin Larsson
>> I was hoping that I could, but it seems that the WAV header has only 
>> fields for WAV.....and the SMV header is in the middle of the file.
>> Xtreme Kommander
> Since detecting SMV would require seeking after WAV file end (size
> specified in RIFF header), it can't be done during probe stage.
> I see three ways here:
> 1) patch WAV demuxer to handle SMV files as well (not nice at all)
> 2) make WAV demuxer detect SMV files and print warning ("hey, use -f smv")
> 3) make SMV demuxer and hope users will add -f smv by themselves
> and there's always
> 0) SMV? What's that?
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I guess I can update the WAV demuxer to print a warning. FFMpeg always 
fails when it tries to decode an SMV file using the WAV codec. So, I can 
add a case where wav_read_header can check to see if the file is SMV, 
and tell the user to force the SMV format.....for now. I'll be working 
on it.

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