doing /;stream.mp3 or /;stream.ogg should do it with a v1 DNAS (as you seem to be using). if using a v2 DNAS then you could do it natively via the streampath option.
however, i hope you're not trying to do as you've actually posted and fool the player into thinking it's getting an ogg stream when it's an mp3 stream (that will not work).
and i assume you're taking into account the massive disparity in what the different html5 audio implementations support when it comes to codec support (or rather the lack of codec support).
-daz
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