[XviD-devel] gmc problem - who to blame?

[Christoph Lampert]

On Wed, 6 Aug 2003, Radek Czyz wrote:

> Hi everyone.
> 
> XviD GMC is sometimes not decoded correctly using libavcodec. An
> example of such clip is at
> 
> http://homepages.ihug.com.au/~syskin/prob.avi
> 
> If you can, could you please check if it's xvid's fault or
> libavcodec's fault?

Hi,

libavcodec reports "|level| overflow in 3. esc, qp=30". 

If I see correctly, GOP is ISPSBBSBBS, and the first S-VOP is 
encoded with QP 30. So the following B-VOPs don't matter, which is 
good for debugging. Nevertheless, can you reproduce this problem without
B-frames? 

Why is the S-VOP encoded at quant 30? That's terribly high compared to
QP=5 for the rest. Also, the frame isn't smaller than the others, so 
maybe simply this quantizer value is wrong? 
Did you use adaptive quantization? Maybe the wrong quant value is written
to bitstream? Can you reproduce the problem with fixed quant? Or at least
for an S-VOP with lower quant? If you set maximum quantizer to 29 e.g. and
reencode exactly the same way. Is then still qp==30 for the wrong frame?
Or does it change?

gruel

******************************************************************
qp:6 fc:1,1 I size:36944 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:30 fc:2,1 S size:42640 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:5 fc:2,1 P size:42048 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:5 fc:1,1 S size:30464 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:12 fc:1,1 B size:3672 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:13 fc:1,1 B size:3696 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:5 fc:1,1 S size:27688 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:12 fc:1,1 B size:4592 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:11 fc:1,1 B size:4928 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:5 fc:1,1 S size:30680 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3
qp:12 fc:1,1 B size:3264 pro:1 alt:0 top:0 hpel part:0 resync:0 w:3 a:3

startcode: 1B5 Visual Object Start at 32
startcode: 100 Video Object Start at 72
startcode: 120 Video Object Layer Start at 104
startcode: 1B2 User Data at 240
startcode: 1B6 Video Object Plane start at 344
startcode: 1B6 Video Object Plane start at 32
startcode: 1B6 Video Object Plane start at 32
startcode: 1B6 Video Object Plane start at 32
startcode: 1B6 Video Object Plane start at 32
startcode: 1B6 Video Object Plane start at 32