[FFmpeg-user] Increasing the decoding speed of yuv444p h.264 files

Claudiu Rad jazzman at misalpina.net
Mon May 18 18:48:05 CEST 2015

On 5/18/2015 7:22 PM, Yan Li wrote:
> I've done some more tests. Input file src.flv is in yuv444p with 48
> fps. I use the following commands to generate two lossless test files:
> 1: ffmpeg -i src.flv -c:v libx264 -qp 0 -preset ultrafast -an yuv444p.mkv
> 2: ffmpeg -i src.flv -c:v libx264 -qp 0 -preset ultrafast -pix_fmt
> yuv420p -an yuv420p.mkv
> Then I test the decoding speed using:
> time ffmpeg -i yuv444p.mkv -f rawvideo -an - >/dev/null
>   - yuv444p.mkv (496 Mb/s): decoded at 55 fps
>   - yuv420p.mkv (336 Mb/s): decoded at 92 fps
> (I/O is not the bottleneck here. Four threads are used.)

sorry to question, but:
are you really sure about this? those are really high bitrates and it 
appears to be a direct link between bitrate and decoding speed: 496 x 55 
~= 336 x 92 (by a 10% margin).
I don't know what's the drive access pattern in this case but if seeks 
just a bit, you have a problem.
as a test, I would encode at much smaller bitrates and then compare the fps.
of course, you can measure the disk I/O load with appropriate tools 
during decoding.


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