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

Moritz Barsnick barsnick at gmx.net
Wed Dec 2 16:12:09 CET 2015

On Wed, Dec 02, 2015 at 15:56:41 +0100, D wrote:
> Maybe it's possible with the -CLI version. I wonder what settings the 
> GUI creates and forwards to x264, so I could take them and just add 
> "-threads n" and see how it scales.

(lib)x264 inserts information about its complete settings into a
private part of the stream, as a human-readable string. Either use
mediainfo, which exposes this, or simply:
$ strings < file.mp4 | grep x264

You will get something like this:
$ strings < someoddfileifound.mp4 | grep x264
x264 - core 142 - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=3 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00

Good luck constructing a command line from that. ;-) At least you can
compare settings, perhaps only two or three differ.


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