Clip a portion of a video

The following command saves a five-second clip from input.mkv to output.mkv.

ffmpeg -i input.mkv -ss 00:05:10.500 -t 00:00:05.000 output.mkv

• -ss 00:05:10.500: start clipping at hh:mm:ss.ms
• -t 00:00:05.000: clip a duration of hh:mm:ss.ms

Remove black borders

The following steps consecutively detects and crops black borders around a video file. This tutorial assumes the aspect ratio of the video is the same across the whole video, i.e., it does not change, i.e., no post-Inception Nolan films.

Detect which areas to crop

ffmpeg -i input.mkv -ss 00:05:00 -t 1 -vf cropdetect -f null - 2>&1 | awk '/crop/ { print $NF }' | tail -1

The command above will utilize ffmpeg’s cropdetect functionality to detect which area to crop. The portion with awk and tail are for ease of usage.

• ffmpeg: the command-line tool
  • -i input.mkv: the video file
  • -ss 00:05:00: start at the fifth minute
  • -t 1: run for one minute
  • -vf cropdetect: use cropdetect video filter
  • -f null: use null muxer; don’t produce output file
  • -: use stdin/stdout (depending on input/output stream)
• awk '/crop/ { print $NF }': print the last column of lines containing the word “crop”
• tail -1: print only the last line

Check if cropdetect was correct

Now check if the dimensions returned by cropdetect is correct. The following command will play the video in the default media player with the video cropped. (Don’t forget to replace the crop dimensions in the command below with yours.)

ffplay -vf crop=960:720:0:0 input.mkv

Crop the video

If the crop dimension is correct, it’s time for actually cropping the video.

ffmpeg -i input.mkv -vf crop=<crop_dimension> -c:a copy input_cropped.mkv