[MPlayer-users] Re: Low bitrate using 2-pass with libavcodec

[Michael Niedermayer]

Hi

On Monday 22 April 2002 04:40, Arpi wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi,
>
> > > pass2.avi has lower quality than pass1.avi having about the same size.
> >
> > Well, an alternate 2pass mode has just been committed to mplayer &
> > libavcodec. Perhaps you can try it ? Be sure to check the latest CVS
> > version of each. I didn't have time to really test it, but it seems
> > better than the old (divxnetwork) code. At least it sticks to the
> > desired bitrate quite well in -pass 2.
>
> nope. -pass still uses divx4 2psss code. to use lavc's one, use -lavcopts
> vpass=1 and -lavcopts vpass=2
>
> my first test is nice, quality is acceptable and for vbitrate=600 i got:
> Video stream:  600.062 kbit/s  (75007 bps)  size: 627774738 bytes  8369.464
> secs
>
> it was vcd sized video, coded with options:
> -lavcopts vcodec=mpeg4:vhq:vpass=2:vmax_b_frames=2:vqmin=2:vbitrate=600
> -vop crop=336:224:16:0
>
> note that blockiness was reduced, but still visible for fats motion scenes
> :( i'll make a test with higher resolution and bitrate tomorrow.
u could try vqmin=7 or lower
or vqcomp=0.6 or higher
or try vb_strategy=1

>
> what's the status of B frame support? it seems to work, but dunno if it
> really helps or it's not yet finished.
it should be finished, but doesnt seem to help much, i need to check how much 
divx really gains with b-frames but thats tricky as they dont support 
constant quantizer encoding with b frames, i first need to reproduce divx 
"constant" quantizer mode in lavc for a comparission (they seem to use much 
higher quantizers for the b frames)
btw, i just noticed that divx 5.01 files dont play correctly in lavc :( ... 
ill fix it asap

[...]

Michael