FFmpeg

Video cropping

snatched from https://stackoverflow.com/a/52675535

ffmpeg -i 'file.mov'  -filter:v 'crop=iw:ih-40' 'file-cropped.mp4'

ffmpeg -y -hide_banner -i "test.avi" -filter:v "crop=iw-400:ih-40,scale=960:720" -pix_fmt yuv420p output_video.mp4

Quick explanation (literal quote from https://stackoverflow.com/a/52675535):
crop=iw-400:ih-40 Cropping 400 from the input width (iw) (2x200 left/right) Cropping 40 from the input height (ih) (2x20 top/bottom) You can cut a little more off if you want a 'crisper' edge.
scale=960:720 Scaling the video slightly to bring it back to your original 720p, the 960 is to keep it at a nice 4x3 ratio. This scaling is not needed, your preference.

Speed up video / Slow down video

snatched from/more information at https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video

# export raw stream without timestamp information
ffmpeg -i input.mp4 -map 0:v -c:v copy -bsf:v h264_mp4toannexb raw.h264

# set timestamp info (set input framerate to 65) and limit output framerate to 30
ffmpeg -fflags +genpts -r 65 -i raw.h264 -c:v  copy -fpsmax 30 output.mp4

Concatenate files / merge files

snatched from https://trac.ffmpeg.org/wiki/Concatenate

list.txt

file '/path/to/file1.wav'
file '/path/to/file2.wav'
file '/path/to/file3.wav'

ffmpeg -f concat -safe 0 -i list.txt -c copy output.wav

Generate GIF

snatched from https://www.bannerbear.com/blog/how-to-make-a-gif-from-a-video-using-ffmpeg/

ffmpeg -ss 23.0 -t 1.8 -i input.mp4 output_trimmed.gif