This is a notes post and may not be as easy to follow as a de facto blog post.
FFmpeg commands I find on the web look insanely confusing even for seemingly simple operations. Here's some stuff I find myself using every now and then.
Convert video file format
This converts a MOV file to MP4, but it should be able to be modified to do any kind of video conversion as long as you know the video codecs for them.
Change Frame Rate
This changes the frame rate of the input video. If the target rate is lower than source rate, it removes some frames. If greater, it probably duplicates some frames: I haven't tried it for that case before.