[FFmpeg-user] libx264 very bad scaling with 4 real CPU cores (no HT)

[Lou]

On Tue, 1 Dec 2015 22:19:16 +0100
D <dcmhoybdpzkh at web.de> wrote:

> I built it with yasm. But $ ffmpeg seems not to display it? Or does it 
> only display it if it's disabled, so mine is enabled?
> 
> ffmpeg version N-76952-g6b978da Copyright (c) 2000-2015 the FFmpeg 
> developers
>    built with gcc 5.2.1 (Ubuntu 5.2.1-22ubuntu2) 20151010
>    configuration: --prefix=/home/username/ffmpeg_build 
> --pkg-config-flags=--static 
> --extra-cflags=-I/home/username/ffmpeg_build/include 
> --extra-ldflags=-L/home/username/ffmpeg_build/lib 
> --bindir=/home/username/bin --enable-gpl --enable-libass 
> --enable-libfreetype --enable-libopus --enable-libtheora 
> --enable-libvorbis --enable-libx264 --enable-nonfree
>    libavutil      55.  9.100 / 55.  9.100
>    libavcodec     57. 16.101 / 57. 16.101
>    libavformat    57. 19.100 / 57. 19.100
>    libavdevice    57.  0.100 / 57.  0.100
>    libavfilter     6. 17.100 /  6. 17.100
>    libswscale      4.  0.100 /  4.  0.100
>    libswresample   2.  0.101 /  2.  0.101
>    libpostproc    54.  0.100 / 54.  0.100

That's not the complete console output. The "using cpu capabilities"
output from libx264 is worth noting.

> If I omit it it's of course the same as "-threads 4" (I did already test 
> it and at least this is what I would expect because I have 4 real cores 
> on a 84W TDP Haswell i5 CPU). See without "-threads 4" down below.

4 cores does not mean that x264 will automatically choose 4 threads.
For example, for my aging i7 860, x264 will use threads=12 (cores*1.5
for frame threads).

I did not read the whole thread, so I'm likely missing something
obvious, why not just use the defaults? Why are you messing around with
threads?

> > In the console output when using the defaults, what value appears for
> > "threads=" in the x264 info? (You may have to output to a file instead
> > of null for it to appear).  
> Don't know how to see it.

Encode a file. Look at the console output; specifically the long line
that starts something like this:

[libx264 @ 0x55be781c6d40] 264 - core 148 r2579 73ae2d1 ...

> > Now for the important question: did you also test the x264 cli tool?  
> Indeed an important question.
> $ sudo apt-get install x264
> 
> $ time x264 --pass 1 --crf 23 --preset ultrafast --threads 1 -o "b.mp4" 
> "a.mp4"
> real    1m33.883s
[...]
> So unfortunately basically the same as with ffmpeg.

In this case your questions should be asked at x264 help resources.