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MP3 is a Container or Codec alone
cernall
post Jul 2 2010, 09:14
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We can se files with MP# extension. Is MP3 a container also, or it is a codec alone?

If its a codec alone, then how can we play and have some meta information in the mp3 files?
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mjb2006
post Jul 2 2010, 22:51
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Answering the original questions... [this is basically just a longer version of saratoga's reply, which came in while I was typing]
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how can we play and have some meta information in the mp3 files?

QUOTE
I'm guessing tags are essentially just extra data in the headers?


MP3 data is just the audio data segments ('frames') which, in series, compose a 'stream'. Each frame has its own header containing technical metadata about that frame (format version, bitrate, stereo mode, etc.), but nothing about the entire stream - no artist, title, etc.; AFAIK that kind of metadata was deliberately omitted from the MP3 spec, perhaps because it was thought that if a container format were needed, a suitable one would be properly developed by the industries that were interested in MP3.

So instead, at least for the way most of use MP3, various ad-hoc, not-very-well-thought-out-or-standardized methods have been devised to append or prepend chunks of formatted data ('tags') to a given stream. The most popular tag format has long been ID3, of which there are several versions, but APEv2 seems to be increasingly popular. These tags are basically garbage (in that they're not MP3 data) on the ends of the stream, but the programmers' maxim "be strict in what you produce and lenient in what you accept" dictates that consumers of ".mp3" files concentrate on whatever MP3 frames are there, and either properly handle or just ignore any garbage—er, tags. You can think of the file as being a 'container', then, but really it's just an MP3 stream possibly with other stuff embedded. Generally, you should expect that any MP3 file you run across will have no tags, or one tag, or many tags, all in different formats, and possibly at inconsistent locations.

This post has been edited by mjb2006: Jul 2 2010, 22:57
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