Remove .mp4 video top and bottom black bars using ffmpeg

FFmpeg cropdetect and crop filters

1. Get crop parameters

cropdetect can be used to provide the parameters for the crop filter. In this example the first 90 seconds is skipped and 10 frames are processed:

$ ffmpeg -ss 90 -i input.mp4 -vframes 10 -vf cropdetect -f null -
...
[Parsed_cropdetect_0 @ 0x220cdc0] x1:0 x2:1279 y1:0 y2:719 w:1280 h:720 x:0 y:0 pts:215 t:0.215000 crop=1280:720:0:0
[Parsed_cropdetect_0 @ 0x220cdc0] x1:0 x2:1279 y1:0 y2:719 w:1280 h:720 x:0 y:0 pts:257 t:0.257000 crop=1280:720:0:0
[Parsed_cropdetect_0 @ 0x220cdc0] x1:0 x2:1279 y1:0 y2:719 w:1280 h:720 x:0 y:0 pts:299 t:0.299000 crop=1280:720:0:0

At the end of each line, you can see it says crop=1280:720:0:0. So according to cropdetect we can use crop=1280:720:0:0.

2. Preview with ffplay

$ ffplay -vf crop=1280:720:0:0 input.mp4

3. Re-encode using the crop filter

$ ffmpeg -i input.mp4 -vf crop=1280:720:0:0 -c:a copy output.mp4

In this example the audio is just stream copied (re-muxed) since you probably don't need to re-encode it.

Also see

  • FFmpeg and H.264 Video Encoding Guide

Crop during playback

As you've seen above with the ffplay example some players allow you to crop upon playback. This has the advantage of:

  • Instant gratification; no need to re-encode
  • The quality is preserved

Tags:

Ffmpeg

Mp4

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