Mark Taylor schrieb am Fre, 09 Jun 2000:
> This bitstreams produced by this mode are just like other
> VBR streams, so there should be no compatibility problems.
>
> To explain how this works, take a 128kbs CBR for example.
> In that case, LAME allocated a base amount of
> bits for each frame. This base amount is about 10% less than
> a 128kbs stream, so that the bit reservoir is slowly built up.
> LAME then allocates extra bits based on the "perceptual entropy",
> computed in psymodel.c. If the perceptual entropy is large,
> the frame can use the base amount + up to 60% of the reservoir.
> These ideas come straight from the ISO docs, but the implementation
> in LAME is new (the ISO dist10 code reservoir treatment is a disaster.)
>
> "Safe VBR" is even simpler: It computes the same base
> amount of bits for each frame, and then computes extra bits
> needed based on the perceptual entropy. But instead of
> relying on the bit reservoir (which might be empty)
> it just increase the frame size when extra bits are needed.
The Safe-VBR mode is more a constant rate encoding than a variable rate
encoding. I made (not in CVS) a switch allowing to specify a target
bitrate with --abr 157 and noticed that 157 kbits would be reached more
often than not. OK that fatboy sample needed a lot more than the target
bitrate ;)
Robert
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