[FFmpeg-devel] [PATCH] raw demuxer for Chinese AVS elementary streams

[Michael Niedermayer]

On Fri, Feb 20, 2009 at 08:16:15PM +0100, Stefan Gehrer wrote:
> Michael Niedermayer wrote:
> > On Fri, Feb 20, 2009 at 07:04:32PM +0100, Stefan Gehrer wrote:
> >> Michael Niedermayer wrote:
> >>> On Thu, Feb 19, 2009 at 09:33:54PM +0100, Stefan Gehrer wrote:
> >>>> Hi,
> >>>>
> >>>> attached patch adds $subject. This makes it possible to test the
> >>>> two samples at
> >>>> http://samples.mplayerhq.hu/AVS/issue767/
> >>>> Unfortunately these samples do not work properly yet, only the
> >>>> I-Frames.
> >>>> You can see that the patch contains a probe function and I was
> >>>> trying to make that probing fairly restrictive. However, my feeling
> >>>> is that a probing function is a slightly dangerous addition unless
> >>>> tested against a large number of samples, which I didn't do.
> >>>> So it might be better to consider the patch for after the release ...
> >>> i think the probe function should be improved a bit more if possible
> >>> for example there are quite a few 0x1XX codes that are neither checked
> >>> for being within a valid range nor trigger detection failure
> >> Okay, choose any combination of further restrictions you like:
> >>
> >> 1. The slice start codes are 0x100 to 01xAF. Since slices in AVS are
> >> whole macroblock lines and the start code represents the vertical
> >> macroblock coordinate, this could be restricted e.g. to 0x43 maximum
> >> to support up to 1088 pixels vertically
> > 
> > is it allowed for a single slice to contain more than 1 row? 
> 
> yes. And there might not be any slice codes at all in a frame, that is
> why I could not take the pic*9<=slice*10 test from mpegvideo_probe.

ok, what about order, may they be in any order or consequtive? if consecutive
then this could be checked for


> 
> > 
> >> 2. 0x1B4 is labelled as reserved in AVS and could trigger detection
> >> failure
> > 
> > yes
> > 
> > 
> >> 3. Bail out if the first byte after 0x1B0 (sequence header, profile_id)
> >> is not 0x20. For all AVS samples I know of it has this value,
> >> corresponding to JiZhun profile.
> > 
> > but does AVS allow other values?
> 
> The spec I have only defines JiZhun profile and it lists for that field:
> 0x00 forbidden
> 0x20 JiZhun profile
> others reserved
> 
> Now as far as I know there is also a "mobile" profile either
> standardized or in the makings, and I could imagine it extending this
> field by using one of the reserved values, but I have no further
> information.

hmm ok then add a check for 0x20, i guess that should be then enough with
some luck

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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