As a general rule you should always edit in the highest resolution that your software supports and only convert it to a lower resolution format, if necessary, after you have completed the editing.

Note that mpeg is merely a container and the actual format will be determined by the codecs the particular version you use has. For use on the web you are recommended to use, at minimum, the avc1.42E01E codec for video and the mp4a.40.2 audio codec as these are always recognised by Apple devices.

note: I locked this topic as it was referring to non-Linux sw and I believe that it is a pre-spam post that will eventually be responded to with link for a proprietary package