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List:       xine-devel
Subject:    Re: [xine-devel] Bug in XShm video output driver or MPEG-2 video decoder
From:       Ewald Snel <ewald () rambo ! its ! tudelft ! nl>
Date:       2003-03-07 22:29:09
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Hi Miguel,

[...]

> lets try to narrow it down:
>
> 1) does it happen only when you hit pause? (it that case it might be a
> problem with frame duplication and copy on video_out.c.)

Yes, and only with the MPEG-2 video decoder. The problem doesn't occur always, 
but very frequent. Just try to play any MPEG-2 file using the XShm video 
driver and hit pause a few times to trigger this problem.

> 2) you said that the slice comes from an old frame, so the image is not
> being overwritten right? i mean, it is more like the new image was
> drawed over a "recycled" frame, but it didn't set the initial slice
> pointer to zero or something?

The entire frame is old, usually about a second ago. The top slice is wrong in 
about 25% of the cases. This could be related to MPEG-2 B-frames, which reuse 
the top slice for video drivers that use 'copy' (see slice.c:1446...1454).

> that's all i can guess now, but i really think you should know the xshm
> driver better than i...

There is at least one problem in video_out.c as well. The 'duplicate_frame()' 
function will copy the raw YV12 or YUY2 samples, which are unavailable for 
MPEG-2 B-frames (top slice is reused). This doesn't explain why the entire 
frame is old, but it should fix at least the invalid top slice problem.

Should I change this in libmpeg2? It might cause a slight performance hit.

> regards,
>
> Miguel

Thanks.
bye,

ewald



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