[x264-devel] VBV Rate Control Challenge

[Mike Kazmier]

All,

I have an interesting test clip which consistently breaks VBV rate control.  In particular, the breakage is worse when using --rc-lookahead.  I find this interesting because I thought lookahead would help with this situation.  The scene is not necessarily one you would find in the wild (in other words, we were setup for failure) but none the less, I would expect x264 to handle it somewhat gracefully.  I am not sure of a strategy to do so beyond improving the heuristics of the lookahead to identify the amazing complex scene (static) that is coming and empty the VBV to the most extent possible while also cranking the QP all the way up.  Any thoughts are appreciated.  You can recreate the vbv underflow with this command:

ffmpeg -i ./doremi-2.ts -f rawvideo -s 1920x1080 -| x264 -o ./doremi-2.h264 --threads 9 --trellis 1 --nr 1000 --bitrate 6500 --vbv-maxrate 6500 --vbv-bufsize 6000 --fps 30000/1001 --keyint 60 --min-keyint 15 --rc-lookahead 0 --interlaced --bframes 3 --b-adapt 1  - 1920x1080

The sample clip is available here:
http://www.mediafire.com/?hljzzzdm2ny

Thanks,

--DaKaZ