Gnu parallel how to use with ffmpeg

You're dealing with a directory of videos, so you will probably need to use a loop. The following loop will split each matched file into ten minute segments, as requested in your comment:

for i in *.mp4; do 
    ffmpeg -i "$i" -c copy \
    -f segment -segment_time 600 \
    -reset_timestamps 1 \
    "${i/%.mp4/_part%02d.mp4}"; 
done

However, if your input is a directory of images, then the image2 demuxer lets you use wildcards. Just specify -pattern_type glob and pass your glob pattern to -i in a non-interpolated string (so that the shell does not expand it).

For example, I did the following when converting a directory of JPEG files to an MPEG-4 video:

ffmpeg -f image2 -pattern_type glob -i '*.jpg' output.mp4

Just be aware that this depends entirely on the glob pattern to determine the order that the matched image files are processed.

GNU parallel solution:

Sample input.txt (for demonstration):

a   b
c   d
e   f

grep '^[ac]' input.txt will be used to emulate command(or pipeline) acting like input source file

parallel -C '\t' echo :::: <(grep '^[ac]' input.txt) ::: $(seq 1 3)

The output:

a b 1
a b 2
a b 3
c d 1
c d 2
c d 3

• :::: argfiles - treat argfiles as input source. ::: and :::: can be mixed.

To aggregate elements from each input source - add --xapply option:

parallel -C '\t' --xapply echo :::: <(grep '^[ac]' input.txt) ::: $(seq 1 2)

The output:

a b 1
c d 2