[x264-devel] multi-process encoding problem

[aviad rozenhek]

On Sun, Jan 29, 2012 at 13:06, Jason Garrett-Glaser <jason at x264.com> wrote:

> On Sun, Jan 29, 2012 at 2:57 AM, aviad rozenhek <aviadr1 at gmail.com> wrote:
> > 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.
>
> Transcode means to decode a video, then encode it.
>
> Decoding 1080p video is vastly more processor-intensive than encoding
> 432x240 video.
>
> You're probably going to be massively bottlenecked by the decoding
> step, which x264 doesn't have anything to do with.
>
> Jason
>

very true.
that's exactly why we are trying to solve the issue by running multiple
instances of the x264 process, each working interdependently on a separate
fragments of the source video. by doing a 5X multi-process encode, we are
effectively decoding and down-scaling with at least 5 threads, thus
bypassing the decode/downscale bottleneck.

however, as I mentioned, we ran into issues with concatenation of the
files, and the issue appears not to be related to timestamps.
is there anything else [such as some magic flags in the first keyframe]
that can explain the "jitter" or "lag" that we experience when playing the
sewn-together output file?

x264 --vf resize:320,240 --ssim --psnr --preset fast --profile high
--bitrate 247 --keyint 75 --vbv-bufsize 741  --no-scenecut  --force-cfr
 --frames 178  -o "ltt.flv.video1.section0.flv" "love_the_taste_1.mpg"

x264   --vf resize:320,240 --ssim --psnr --preset fast --profile high
--bitrate 247 --keyint 75 --vbv-bufsize 741  --no-scenecut  --force-cfr
 --seek 178  --frames 192  -o "ltt.flv.video1.section1.flv"
"love_the_taste_1.mpg"

x264   --vf resize:320,240 --ssim --psnr --preset fast --profile high
--bitrate 247 --keyint 75 --vbv-bufsize 741  --no-scenecut  --force-cfr
 --seek 370  --frames 192  -o "ltt.flv.video1.section2.flv"
"love_the_taste_1.mpg"

x264   --vf resize:320,240 --ssim --psnr --preset fast --profile high
--bitrate 247 --keyint 75 --vbv-bufsize 741  --no-scenecut  --force-cfr
 --seek 562  --frames 192  -o "ltt.flv.video1.section3.flv"
"love_the_taste_1.mpg"

x264   --vf resize:320,240 --ssim --psnr --preset fast --profile high
--bitrate 247 --keyint 75 --vbv-bufsize 741  --no-scenecut  --force-cfr
 --seek 754  -o "ltt.flv.video1.section4.flv" "love_the_taste_1.mpg"

-- 
Aviad Rozenhek
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