[FFmpeg-user] Linux PC Locks Up When Encoding Video

[James Board]

I'm trying to encode video that I captured from a BlackMagic capture card. 
The input format is MJPEG.  The ffmpeg encode command is
    ffmpeg -i IN.avi -c:a copy -c:v libx264 -vf eq=brightness=0.05 -preset medium -crf 20 OUT.avi
This command intermittently locks up the PC: if i repeatedly try to encode the same10-minute segment,sometimes the encode works, however it usually fails within an houror so.  When that happens, the screen is frozen and I have to power cycle toreboot.  This problem occurred on an Intel CPU running Ubuntu 16.  I then installed 
Ubuntu 18 and the problem still occurred.  The same input file encodes successfullywith ffmpeg on a different machine (so I think the input file is okay).  I'm using thecurrent ffmpeg snapshot built from recent source.  This problem also occurs using apre-built ffmpeg binary from a few months ago: ffmpeg-4.1.2-amd64-static 
First Question: Does anyone know why this happens, how to fix it, or how to determine 
why this is happening?

Second Question: I know my GPU on this machine has problems.  Does ffmpeg orlibx264 use the GPU when encoding?  If so, can I tell ffmpeg not to use the GPU?