Fwd: Re: Low cost remote stereo feed to FM station
Tue May 8 11:12:11 EDT 2007
>The Barix boxes use VBR MP3's, and for a stereo feed "broadcast
>quality" demands about 112 to 128kbps of bandwidth. Mono feed requires
>half as much bandwidth. All MP3's will need that.
Why VBR? If the source audio changes characteristics, the required
bitrate could increase, making the bandwidth requirement a tad
unpredictable. Unless, for example, the upper limit of the VBR is
clamped. Would ABR manage the bandwidth better?
Actually by definition VBR manages bandwidth better since in the case of
reduced available throughput it will throttle the bitrate rather than
dropping out and rebuffering.
But to answer your question, I don't know exactly why they only use VBR
but it is kinda annoying. Especially in the method they implement it;
you enter a number between 0 and 7 and each number corresponds to a
bitrate range that the VBR will limit itself to. It's actually unable
to encode at bitrates lower than about 60kbps which is pretty high for mono.
I assume it's got something to do with codec licensing...it's not cheap
to license MP3 codecs (nor particularly easy to do it "safely" with all
the lawsuits flying around about who really "controls" the MP3 licensing)
Boston, MA 02446-2204
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