Video settings or codecs are a minefield. Store your original ISO files securely and make sure you have copies. I can also recommend Handbrake, but you may need to play around with the settings a bit to find something that fits your use. Just keep in mind that any conversion means a (slight) loss of quality, which is why saving the original ISO files is useful. The other thing is that the file format, be it MP4, MKV or something else, is what's called a container format. It's just a container that holds both video and audio as well as other stuff (sometimes) and the internal bits can have many different attributes depending on the settings chosen for the conversion. I'm no expert, but a H.264 encoded video stream is something that most bits of software and hardware should be able to play back these days.