[XviD-devel] Scenechange detection

Christoph Lampert chl at math.uni-bonn.de
Wed Dec 31 10:55:48 CET 2003


I tested XviD on a longer sequence of smaller images, 256x196
and when I looked at keyframes and actual scenechanges, they
didn't coincide very well. 
I mean, it's not a big deal, because XviD doens't really aims for
making scenechanges keyframes, but rather those frames where lots 
of INTRA-MBs are, but in fact I had both:
scene changes which were not I-frames and I-frames in which nothing
spectacular happens at all! And that was not only the uses due to
max_keyframe-interval, of course. 
Could there be a problem in I-frame decision, maybe SKIP blocks counted
wrong or so? 
Also, the sequence had letterbox black bars of height 32 each, and 192 is
not a multiple of 16, but internal was 204, so the black bars covered
almost 30% of the internal image. This makes it very difficult to reach
50% of INTRA blocks, right? 
Should we compensate for this somehow, or should we just ignore it? 

Have any of you checked and/or noticed problems with keyframe detection?


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