[FFmpeg-devel] AC3 Format Detection unreliable.

Michael Niedermayer michaelni
Sun Aug 5 04:14:47 CEST 2007


On Sat, Aug 04, 2007 at 08:33:03PM -0400, Justin Ruggles wrote:
> Justin Ruggles wrote:
> > Dan Sully wrote:
> >> * Dan Sully shaped the electrons to say...
> >>
> >>>> Yes, please make the stream(s) available.
> >> Also, I am on an amd64 system.
> > 
> > Doesn't look like that's an issue.  I'm getting the same thing on my 
> > system.  The file is valid.  The issue seems to be the frame size. 
> > 640kbps 48kHz is the largest AC3 frame size, and I think it's not 
> > fitting enough frames into the probe buffer to give a positive 
> > detection.  I'll look into it.
> The problem with this sample is two-fold.  The first issue is that the 
> probe buffer in this case is only 2048 bytes.  The frame size for this 
> sample (and any others which are 640kbps & 48kHz) is 2560.  Therefore, 
> only 1 frame is detected.  I changed the threshold for a score of 50 
> down to 2 frames, but this doesn't help here.  After I changed to 1 
> frame (at the start of the stream) it now gets a score of 50, but then a 
> 2nd issue occurs.
> The sample is misdetected as MPEG-PS because it gets a score of 52 from 
> mpegps_probe() for some odd reason.  I don't know a whole lot about the 
> MPEG-PS format, so I don't think I can figure that part out...

feel free to revert the parts of your changes to ac3_probe which made it
an omnivore

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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