[XviD-devel] VBV into CVS HEAD

[Christoph Lampert]

Hi,

sorry for the big delay, now I finally committed VBV to CVS HEAD. 
As I wrote the last time when I committed to the wrong place, it's 
mainly in the 2pass encoding plugin, because 2pass the place where it 
belongs. 
VBV is activated by setting 2pass-parameter vbv_size (from xvid.h)
nonzero. Typical values (DivX Home Theater) are
		rc2pass2.vbv_size     =  3145728;
		rc2pass2.vbv_initial  =  2359296;  // 75% of vbv_size
		rc2pass2.vbv_maxrate  =  4000000;
		rc2pass2.vbv_peakrate = 10000000;

Since default is 0 for all unknown parameters, default for VBV is OFF.

Please test, especially with difficult material, like high action, 
explosions, long fades...

gruel

P.S.

I attached a small plot of vbv control in action: Red is the first pass, 
green the second without VBV, blue the second with DivX Home Theater VBV. 
Max bitrate is 4000 kbps, which corresponds to the 200000 bit level. 
As you see, there is a very difficult scene starting at frame 400. With 
quant 2, bitrate goes up to far over 10000 kbps! 
Target bitrate was 3000kbps. Normal 2nd-pass encodes at much higher 
bitrate than 4000kbps for almost 200 frames. That's too much data for a 
too long time, the VBV conditions will be violated and hardware players 
might not catch up with reading from disk. 
VBV keeps track of total data, and reduces bitrate after a while such 
that VBV is fulfilled and buffer don't run empty. Bitrate can go over the 
max of 4000 kbps, but not for too long. 

The disadvantage is that the quantizer is raised if very difficult 
scenes go on for too long. This cannot really be avoided, if we want to be 
VBV compatible (although I have some ideas how to get rid of it). However, 
usually these scenes can tolerate higher quants rather well. 
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