[x264-devel] Bug with flashing scene

[BugMaster]

On Sat, 19 Apr 2014 00:26:03 -0400, David Mackenzie wrote:
> Hi x264 devs,

> I'm encoding some animated content, and this scene produces some
> very bad distortion on the output during a sequence where the screen
> flashes black and white (frame 55).

> You can grab the source file (UTvideo AVI format) and the x264 encode showing the problem here:

> http://mab.to/fr5KCBOTJ

> I've tried this on several different software players, it doesn't
> seem to be a bug in the decoders (all replicate it exactly). Have
> yet to burn it to disc and try it on a set-top player though.

> Forcing the affected frame to be an I-frame (with "K -1" in the
> QPfile) does work around the error.

> Command line used:

> x264.exe --aq-strength 0.4 --bitrate 30000 --preset veryslow --tune
> film --bluray-compat --vbv-maxrate 40000 --vbv-bufsize 30000 --level
> 4.1 --keyint 24 --open-gop --slices 4 --colorprim "bt709" --transfer
> "bt709" --colormatrix "bt709" --sar 1:1 --qpfile
> "c:\autovenc\tickets\inprog\scherzo_inferna.avs_ticket.chaps"
> --stats
> "c:\autovenc\tickets\inprog\scherzo_inferna.avs_ticket.stats" --pass
> 1 -o
> "G:\Authoring\xxx\D1_Shorts\Asset\secondBatch\scherzo_inferna_bug.avc" "f:\scherzo_inferna.avs"

> Thanks as always for your work on this outstanding encoder.

Hi. Looks like I find out what was causing such artifacts in your
stream. For some reason this black frame was decided as B-frame at
1-st pass while its reference P-frames wasn't black so differed a lot
and due this optimal encoding for most of MBs in this frame was intra
mode but its analyze for historical reasons was disabled for B-frames
in lookahead. This caused big misprediction of size and misbehaviour
of VBV. Try with attached patch which should fix this problem.
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