[XviD-devel] vbr module

[Edouard Gomez]

Hello,

i'm  testing the vbr  code again  and again  and i'm  very disapointed
because the normal curve treatment (no alt cc) never sticks to desired
size. Some times i get undersized files and other times oversized...

I've ploted a typical graph  of the overflow variable of the algorithm
and the encoded vs expected framesizes.

http://perso.wanadoo.fr/ed.gomez/files/overflow.png
http://perso.wanadoo.fr/ed.gomez/files/framesize.png

First graph comments :

As   you'll   see,  the   overflow   gets   crazy   around  the   1700
frame... moreover, the KFoverflow variable  is always == 0 (this can't
be seen in the graph but in my debug output :-)

I don't  understand why the overflow  is getting so  much during these
frames.

2nd graph comment :

As you  can see the expected  graph is respected  *but* many keyframes
are undersized. And we can see a big giant framerate pic at frame 3800
with  a  delay  to  the  previous  expected  iframes...  really  weird
behaviour there.

Conclusion :

I suspect the code to be buggy because of the KFoverflow == 0 all test
long and the too small keyframes encodings. I will post the code soon,
so if someone want to test it and debug it... he would be welcome.

cheers

PS  :  using the  vfw  defaults except  for  max_framesize  == 150%  *
computed_average_frame_size   and   twopass_max_bitrate   ==  150%   *
computed_average_bitrate. Is this wrong ?

--
Edouard Gomez