 MPEG-1 Part 2 video is rare nowadays, and this extension typically refers to an MPEG program stream (defined in MPEG-1 and MPEG-2) or MPEG transport stream (defined in MPEG-2).Other suffixes such as .m2ts also exist specifying the precise container, in this case MPEG-2 TS, but this has little relevance to MPEG-1 media..mp3 is the most common extension for files containing MP3 audio (typically MPEG-1 Audio, sometimes MPEG-2 Audio).