[MPlayer-users] 2 pass divx encoding from .VOB/dvd - Targeted filesize (bitrate) ends up way way wrong

[Michael Niedermayer]

Hi

On Monday 19 August 2002 23:01, D Richard Felker III wrote:
[...]
> -lavcopts vqmin=2, or even 1 perhaps with bitrates this high.
vqmin=1 is NOT recomanded, there are very serious quality issues as the 
dequantized coefficients tend to cause considerable IDCT drift (try to decode 
a file encoded at vqscale=1 with some other decoder, xvid for example)
so if u use vqmin=1 u MUST use vlelim=-4 && vcelim=-4 or lower, these seem to 
reduce these errors but much more testing is needed before we should recomand 
vqmin=1 or vqscale=1, indeed i have serious doubts that there would be a 
vissible quality difference between 1 & 2 assuming that 1 is working

> Actually, I believe there *is* a bug in libavcodec where it won't
> properly distribute bits on the second pass when the minimum qscale
> (vqmin) is already reached on lots of frames, so quality still won't
> be ideal, but it should be a lot better.
hmm, one possible bug is with the fps, lavc ratecontrol calculates the bitrate 
by counting the encoded frames & using the framerate but if this isnt 
constant or something then the bitrate could be wrong

btw, its much easyer to fix bugs which i can reproduce, sadly i cant, and 
noone sended me a video which triggers it :( (yes i know that most of these 
videos are too huge to upload)

[...]

Michael