On Jun 28, 2009, at 6:00 PM, Marta Edie asked:
And one questions begets another: what is the difference between mp4 and mp3 . Methinks that somehow i cannot send files easily when they are in mp4.
There's a computer industry committee, formed in the late 1980s called the Motion Picture Experts Group (a.k.a. MPEG). Their job is to define standards for compressing and encoding sound and video for playback on computers. They've come out with a series of definitions called the MPEG standards.
Their first set of standards is called MPEG-1 and came out in the early 1990s. The ubiquitous mp3 sound files are technically MPEG-1 Level 3 sound files.
In the late 1990s, their fourth revision was issued and was called (big drum roll!) MPEG-4. The mp4 sound files are one type of sound file under the MPEG-4 umbrella. I think the mp4 and m4a files are the same, and Apple seems to use both extensions. Apple uses m4b when the mp4 files are bookmarked, such as with audio books and some podcasts.
In theory, mp4 files should be playable on any platform, as long as modern software is installed. Problems arise because mp4 is really a container format rather than a sound format. This means that there are several different ways to encode and compress the data contained therein. These different methods are called codecs. Not all developers choose to support all the standard codecs.
It is an interesting tidbit that the MPEG-4 specifications were largely based on Apple's QuickTime and Apple holds several important patents for ideas used in MPEG-4.
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