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

Stefan Gehrer stefan.gehrer
Fri Feb 20 20:16:15 CET 2009

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.

>> 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


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