Another app worth checking out is Handbrake, which is available for macOS, Linux and Windows. It is free and open source.
I tried Handbrake a while ago, but from what I remember it always re-encodes and doesn't really do lossless conversions even when it should be possible (i.e. moving a video stream from an .mkv container format to .mp4, etc)
That's true, though it does afford many people a relatively easy way convert. Tools like ffmpeg will offer better options, but the need for command-line knowledge will put it out of the reach of many people.