Any MPEG2 program (=system) stream that conforms to the standard should be accepted by Arbil, provided that the file extension is .mpeg
MPEG4 is a bit more complicated, the current stable Arbil only accepts MPEG4 files with H.264 video, AAC audio and a “hinting track” that are created with QuickTime. The testing and pre-testing versions of Arbil should also accept files that are created with ffmpeg (H.264 video and AAC audio, hinting track no longer needed).
Note that these file type restrictions are relevant mostly for people who archive their data in The Language Archive. If you are using Arbil just to organize your own data, you could choose to override the file type restrictions.