[Ffmpeg-devel] qprd plus bframes = low quality

[Trent Piepho]

Corey Hicket wrote:
> Trent Piepho wrote:
> > Using qprd with b-frames seems to give much lower quality than either b-frames
> > or qprd alone.
> >
> > You can see sample pictures and command line here:
> > http://www.speakeasy.org/~xyzzy/qprd_b.html
>
> > vcodec=mpeg4:vbitrate=6950:dia=-4:predia=8:precmp=2:subcmp=2:cmp=2:v4mv:qpel:lmin=1:vpass=1:vqmin=2:mbd=2:trell:cbp:mv0:dc=8:sc_factor=4
> >
> > with vmax_b_frames=2 and/or qprd added.
>
> Unless Michael steps in and sees immediately what is wrong, I suggest
> that you try to (a) try to simplify your lavcopts, (b) provide a sample
> source video, and (c) provide the full command line. At the very least,
> post the full output of mencoder.

Ok, I've simplified the lavcopts:
vcodec=mpeg4:vbitrate=6950:mbd=2 + vmax_b_frames=2 and/or qprd

I've updated the same page, http://www.speakeasy.org/~xyzzy/qprd_b.html,
with new screenshots created with these options.  I think low quality of
qprd+b-frames is now even more apparent.

Providing a sample video will be difficult.  It's a 19mbit ATSC TS stream
and I don't have space to host more than a few seconds of it.  Even if I
did, I'm using a complex filter chain including multiple filters I wrote,
with an mencoder that has been modified to pass pts through to filters
(mine need that) and deal with 60p->24p conversion better.  So no one would
be able to duplicate my encode anyway.  xvid, lavc mjpeg, lavc ffv1, etc.
all work fine, it's just lavc+mpeg4 that's having problems.

I could create a clip encoded with a lossless codec, like ffv1, which
should let someone duplicate the encoding with any extra software.  But it
will be large, about 190 MB for just 30 seconds.  I can upload it, but not
host it as I only have about 10 MB of web space.  I'll see if it's possible
to duplicate the problems with something encoded with
vcodec=mjpeg:vqscale=2, that should be more manageable in size.