Re: How to identify QPel and GMC flags in an .avi file?

Thanks Chris, I'll try that.

Regards from
VJ

----- Original Message ----- 
From: "Christoph Lampert" <[email protected]>
To: "xvid" <[email protected]>
Sent: Thursday, November 04, 2004 11:28 AM
Subject: Re: [XviD-users] How to identify QPel and GMC flags in an .avi
file?


> On Thu, 4 Nov 2004, VJ wrote:
> >     Is there a command line program for linux or some tip on how to
write
> > such a program to get qpel/gmc flags in an avi file? I need to separate
my
> > collection of 300 avi files so that I may find the ones which can be
played
> > on my Divx/DVD Player. The player does not support qpel/gmc.
>
> You can use mplayer with libavcodec's debug-output, like
>
> mplayer test.avi -lavdopts debug=1 -vo null
>
> you'll get lot's of line, some looking like this
>
> [mpeg4 @ 0x868ff00]qp:5 fc:2,1 P size:1040 pro:1 alt:0 top:0 hpel ...
> [mpeg4 @ 0x868ff00]qp:7 fc:3,3 B size:80 pro:1 alt:0 top:0 hpel ...
> [mpeg4 @ 0x868ff00]qp:5 fc:2,1 P size:1024 pro:1 alt:0 top:0 hpel ...
> [mpeg4 @ 0x868ff00]qp:7 fc:3,3 B size:80 pro:1 alt:0 top:0 hpel ...
>
> If there's a "hpel" in there, then the frame is halfpel, if it's a "qpel",
> it's quarterpel. This is not allowed to change between frames, so
> you can rely on the values from the first frame for the whole
> sequence.
> However, there might be some (incompatible) streams out there which are
> Qpel in one part and Hpel in another. XviD was able to create such beasts
> for a while...
>
> For GMC, it's less clear. If there are any 'S' entries before
> the "size:", then it's clearly a GMC-sequence, because S-VOPs are only
> used for GMC. If there are only 'I', 'P' or 'B', then no GMC is used.
> However, GMC usually is rather rare, and it could very well be that there
> are a couple of thousand IPBs before an S pops up. I don't know of any way
> to check this in advance, since the MPEG-4 header only specifies the
> profile, and most files are in Advanced Simple Profile by now, which
> does allow GMC.
>
> chl
>
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