[FFmpeg-devel] [RFC] per format probe buffer sizes

Kostya kostya.shishkov
Tue Apr 15 19:32:57 CEST 2008

On Tue, Apr 15, 2008 at 06:58:06PM +0200, Michael Niedermayer wrote:
> On Tue, Apr 15, 2008 at 06:06:33PM +0200, Benjamin Larsson wrote:
> > Hello, while trying to work out how to get dts in wav detection to work 
> > properly I found out that there was a problem with the size of the probe 
> > buffer. Right now it starts from 2048 and increases the size until a 
> > format is detected. And when the wav format is used with a command line 
> > like "ffmpeg -i dts.wav test.wav" the format is detected in the first 
> > try. And reliable dts detection in a test file I had will need more. It 
> > found the first SYNC word after 3072 bytes. So for this to work we need 
> > to increase this buffer, one could either do it globally or just for the 
> > needed format. Before the actual probing that finds the wav format 
> > (utils.c:447) there is another probe (utils:433). My suggestion is that 
> > we add a flag and size parameter to the format struct and let this probe 
> > call fetch this value so it can be used later in the real 
> > probe(utils.c:447). This way we can add per format probe sizes which 
> > might useful.
> > 
> > So what do you think of this idea ?
> First i think it is wav and it should use the wav demuxer. And i would like
> to hear some argument why this cant work that way.
> Second you can add a
> if(size<4567) //dts needs that at least so wav - dts differntiation is possible
>     return 0;
> in the wav probe function to achive what you want

My suggestion was something similar - provide flag and desired probe size so
probe function won't even try that format unless probe buffer size is big enough.

Of course it can be done with checking of AVProbeData.buf_size inside read_probe()
but that's a bit hacky IMO and not proof against possible future changes.
> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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