Apple - How can I crop a video?
Handbrake is the way to go here, as mentioned by roguesys and canary_in_the_data_mine in the accepted answer.
I am using Catalina. MPEG Streamclip does not support this version of OSX, and iMovie's cropping tool is married to the 16:9 aspect ratio.
As soon as you open your clip, if it has black bars (which was my case), handbrake will crop them automatically and it will show you in its summary how the converted video will look like.
You can tweak out things in the other tabs (dimensions where you can do a fine tune of the cropping, video for the compression codec and other things, filters, audio, etc).
Once you're satisfied with the settings in the summary, go to the bottom of the App window, choose the folder where you will save the video, and press the green Start button at the top.
If you are using MacBook or iMac the best app is iMovie.
- Create new project in iMovie
- Import video to iMovie and then drag and drop it in your new project
- Select you video in project and use crop button in preview window
- Export your new video and use it
If it is a large file that you need a small part of then first trim the video by pressing command+t when the file is opened in quicktime. Import time to iMovie will decrease by a lot
It's kind of hacky, and probably not the best answer but works if you don't want to download any other tools and just use quicktime, and since I love hacks...
- Open video in Quicktime.
- Select new screen recording from file menu.
- Setup audio source to be built in input from the arrow next to the record button.
- After pressing the record button, Select the area you want to record (instead of doing full screen) in the original video.
- Start the recording.
- Start the original movie playback.
- When original movie finishes stop the recording by clicking the Stop button in the menu bar.