While similar in name, these two file types are very different. MP3 stands for MPEG-1 Audio Layer III, and it is an audio-only container. This format compresses audio files for an easy and versatile way to store sound bites and music. An MP4 (MPEG-4 Part 14), on the other hand, is a multimedia container that can store audio, video, still images, subtitles, and text.