[x264-devel] multi-process encoding problem

[aviad rozenhek]

Dear Experts,

we're using x264 CLI to transcode 1080p video to 240p, using default
setting [--vf resize:432,240]
we noticed that the transcode was slow, achieving only ~70fps on an 2-cpu,
8-core E5520 "Gainestown" machine, while utilizing only a very small
portion of the available CPU.
my analysis led me to think that the bottleneck is the down-scaling stage.

to increase the encoding speed, we ran 4 instances of unmodified x264 in
parallel, each working on a fragment of the original source media, using
the exact same parameters and settings.
after all x264 instances have finished, we concatenated the output files
using avconv, while taking care of [hopefullly] correctly setting PTS and
DTS for the combined file.
this achieved the desired 100% cpu utilization.

Unfortunately we still have an issue when playing the file, where a small
"jump" or "lag" is just noticeable at the exact location where these
separately encoded files were sewn together.
as far as we can tell, all PTSs and DTSs are correctly increasing.

is there some information in the first SPS, PPS or keyframe that could
cause this effect? maybe by causing the decoder to reset itself somehow?
we would be happy to share a small input/output sample [through
datafilehost.com or any other method] along with full command-line and logs

Many thanks,

-- 
Aviad Rozenhek
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