[MPlayer-users] lavc psnr mixup

D Richard Felker III dalias at aerifal.cx
Wed Sep 8 04:57:43 CEST 2004

On Tue, Sep 07, 2004 at 03:48:01PM -0700, Loren Merritt wrote:
> The PSNR values in the psnr_*.log generated by mencoder/lavc seem to be
> matched up to the wrong frame numbers. This occurs consistently on all
> input videos and all lavcopts, including different vcodec's.
> The offset is (3 + vmax_b_frames), and happens in display order, even
> though stats are output in encoded order.
> The other stats (qp, size, frame type) are matched to the correct
> frame number.
> The PSNRs that get bumped off the end due to this offset are not used
> when calculating the PSNR summary printed by mencoder, but the "inf"s
> inserted at the beginning are also not counted in that summary.
> I had a quick look in the source, but couldn't find anywhere (either
> in ve_lavc.c or in libavcodec/) that the psnr computations referred to
> any frame other than the current.

rotfl!! i bet this bug causes the infinities (which get rounded down
to 100 or something) to get averaged into the final psnr, giving the
illusion that B frames improve quality. i also bet that if you fix
this bug, it will be revealed that B frames suck and greatly reduce
psnr... :)


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