>
> Hello,
>
> I just compiled the newest alpha, and was testing the new vbr mode.
> I decided to like it (_a lot_), since it's 3x faster than --vbr-old (!!).
>
> I did some reading up on the list, but I cannot find an answer to
> some Q's, maybe someone can address them, thanks
>
> 1- What was the reason/goal of the new VBR? (speed?, different V1->V9 scale?)
>
Hi Roel,
You should be able to find discussions of this in the mp3encoder
archive, but here is the short answer:
old-vbr calls the CBR algorithm many times with different amounts of
bits until it finds the smallest number of bits which give a
quantization with the given "quality".
new-vbr just computes the scalefactors needed for every critical band
to achieve the given "quality", and then encodes the frame only once
with the computed scalefactors.
"quality" is in quotes because the quality measure is just
formula and is only loosly related to percieved audio quality :-)
Both vbr modes use the same measure of "quality".
> 2- Same kind of bug here (I think) than in the --vbr-old (which was fixed by
> Robert in no time :)):
>
> E:\lame-alpha>lr -V1 -mj -h -b128 teenyweenytinybug.wav
> LAME version 3.86 (alpha 1) (www.sulaco.org/mp3)
> Encoding teenyweenytinybug.wav to teenyweenytinybug.wav.mp3
> Encoding as 44.1 kHz VBR(q=1) j-stereo MPEG1 LayerIII ( 6.0x estimated) qval=2
> Frame | CPU/estimated | time/estimated | play/CPU | ETA
> 53/ 53(100%)| 0:00:01/ 0:00:01| 0:00:01/ 0:00:01| 1.6798| 0:00:00
> ----- bitrate statistics -----
> [kbps] frames
> 32 43 (79.6%)
> 40 4 (7.4%)
> 48 1 (1.9%)
> 64 1 (1.9%)
> 80 2 (3.7%)
> 112 1 (1.9%)
> 128 2 (3.7%)
>
> So again, "-b128" ignored and this time in just about all mp3's, not
> only this one:
This .wav file is mostly silence, and LAME ignores the minimum
bitrate when it detects analog silence.
For non-analog silence, LAME will (with -b128) ensure that each
granule is encoded with the number of bits associated with a
128kbs frame. However, because some of the bitreservoir,
sometimes this data can actually be fit into (for example) at 96kbs
frame. To force all frames to be 128kbs or higher, you need to add
-F (not recommended except in special cases)
Mark
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