Comment 25 for bug 1970674

Test sub2video is taking 9 hours.

Stack trace:
(gdb) i s
#0 0x00007fff62bf5974 in clock_gettime ()
#1 0x00007f88bdf30d06 in __GI___clock_gettime (clock_id=clock_id@entry=1, tp=tp@entry=0x7fff62bdeea0) at ../sysdeps/unix/clock_gettime.c:115
#2 0x00007f88be7fa8d1 in av_gettime_relative () at src/libavutil/time.c:64
#3 0x000055cb53c4c782 in transcode () at src/fftools/ffmpeg.c:4621
#4 0x000055cb53c4c782 in main (argc=<optimised out>, argv=<optimised out>) at src/fftools/ffmpeg.c:4840

I wrote a command that, if the test run time reaches 12 hours, the test process is terminated and, after 10 minutes, killed.