ffmpeg script only running for first in list?

Question

I wrote a small script that converts HQ video to LQ:

ls video/hq | cut -d. -f1 | while read line ; do
  HQ=./video/hq/$line.mp4
  LQ=./video/lq/$line.mp4
  ffmpeg -i $HQ -crf 40 $LQ
done;

When I run ls video/hq | cut -d. f1 I get back:

1502460615677
1502461135975
1502461292963
1502461373947
1502461493936
1502461782119

But when running the conversion script only 1502460615677 is processed.

If I replace the line with ffmpeg with echo $line echo runs for all but with ffmpeg it only runs for one.

Anyone know why ffmpeg changes how this runs?

Aside from parsing ls I don't see a problem. Add set -x to see what commands are actually running. — glenn jackman
– glenn jackman, Commented Aug 11, 2017 at 15:11
@glennjackman before ffmpeg runs I get +read line and then the script ends so no new information. — Philip Kirkbride
– Philip Kirkbride, Commented Aug 11, 2017 at 15:16
@glennjackman strange if I switch my ffmpeg command for echo it works fine. It seems like ffmpeg breaks out of the loop or something(?) — Philip Kirkbride
– Philip Kirkbride, Commented Aug 11, 2017 at 15:22

Philip Kirkbride · Accepted Answer · 2017-08-11 15:27:36Z

2

Apparently ffmpeg reads from standard input, which interferes with the read command. So I'm directing to /dev/null

ls video/hq | cut -d. -f1 | while read line ; do
  HQ=./video/hq/$line.mp4
  LQ=./video/lq/$line.mp4
  ffmpeg -i $HQ -crf 40 $LQ < /dev/null
done;

answered Aug 11, 2017 at 15:27

Philip Kirkbride

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