ffmpeg

# to=timestamp
ffmpeg -i input -ss 00:01:00 -to 00:02:00 output 

# t=duration
ffmpeg -i input -ss 00:01:00 -t 00:02:00 output

# concat
ffmpeg -i "concat:input1.ts|input2.ts|input3.ts" -c copy output.ts

# convert all files in dir from srt to vtt
for file in *.srt; do ffmpeg -i "$file" "${file%.srt}".vtt; done

# extract frame from video to jpg in all files in directory
for file in *.mp4; do ffmpeg -i "$file" -ss 00:00:59.000 -vframes 1 "${file%.mp4}".jpg; done