At a fundamental level, you can specify the type of a media file using a simple Mime type, such as video/mp4 or audio/mpeg. However, many media types—especially those that support video tracks—can benefit from the ability to more precisely describe the format of the data within them. For instance, just describing a video in an MPEG-4 file with the Mime type video/mp4 doesn't say anything about what format the actual media within takes....a media file using a simple MIME type, such as video/mp4 or audio/mpeg...video in an MPEG-4 file with the MIME type video/mp4 doesn't say anything...