We're getting there!

From Jon Udell: Random access to Web audio:

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According to this comparison of HTTP 1.0 and 1.1, the URL parameter idea ran afoul of HTTP 1.1's conditional GET feature, and so byte ranges migrated into the realm of HTTP headers.

To sum up, an ordinary downloadable MP3 sitting on a conventional Web server (as opposed to a streaming MP3 hosted on an Icecast or Shoutcast server) is perfectly able to be randomly accessed -- but only by means of HTTP Range headers, not by means of parameterized URLs. And some (but evidently not all) MP3 players are prepared to exploit that random-access feature

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