Save a preview image from video

ffmpeg -i input_file.mp4 -ss 01:23:45 -vframes 1 output.jpg

Convert .mov to .mp4

ffmpeg -i input.mov -q:v 0 output.mp4

Remove letter box and scale video from mov to mp4

ffmpeg -i hero-video.mov -vf "crop=2880:1616:0:92,scale=720:-1" -c:a copy -vcodec h264 -acodec mp2 -crf 24 output-crop-720.mp4