> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
>
> Given a high bitrate encoding of a track, is there a good way
> to produce a
> lower bitrate encoding from it?
lame --mp3input -h -b 96 highbitrate.mp3 lowbitrate.mp3
> Does MP3 data allow
> mathematical magic to
> produce a lower bitrate file without having to go back out to
> a WAV file
> and be re-encoded? For example, if data is encoded at CBR
> 192, is there
> some transformation on the data that can quickly give CBR 96?
No. There are some small savings that can be made, but the most expensive
parts of encoding (quantization, psychoacoustics, bit packing) need to be
completely redone for best results. You can't simply "throw more bits away".
:)
> And if encodings are made from other encodings, are there
> artifacts that might appear?
Yes, because the encoder no longer has access to the original data - the
psychoacoustics will be comparing to data that is already "damaged". If
you're lowering the bitrate to 96kbit/s, you're likely to get some
distortion anyway; this will only make it worse.
An MP2 developer at Philips advised me that if you intend to cascade code
MP2 data, you should use an initial bitrate about 20kbit/s higher than you
would normally use. I'm not sure what the corresponding figure would be for
MP3, but it's better to avoid cascaded coding entirely.
-- Mat.
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