[Ffmpeg-devel] H.264 decoding bug in either lavc/JM (x264 too?)
Mon Jul 25 18:25:42 CEST 2005
On Fri, 22 Jul 2005, Tuukka Toivonen wrote:
> I encoded a video clip using x264 and decoded with both
> Mplayer (lavc) and JM 9.6. The two decoded videos differ
> slightly on some frames. I think this is bug, as
> H.264 should be bit exact, shouldn't it?
> Here's frame-by-frame comparison:
> x264 command line:
> --bframes 2 --8x8dct --b-pyramid --qp 26 --direct spatial
> The problem occurs only if using all three options --8x8dct, --b-pyramid,
> and --direct spatial. Most other options seem not to matter.
h264.c:1207 should fall back to h->ref_list.motion_val[b4_xy] if
h->ref_list is a B-frame and the colocated block is L1 predicted.
I can't see what 8x8dct would have to do with it.
> For now, for encoding with x264, --direct temporal
> should be used (it increases bit rate around 3% at fixed
> PSNR, but removing --8x8dct or --b-pyramid has larger
> impact, 4-5%).
btw, I think the 3% penatly goes away if you use --ref > 1.
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