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MP3 Bit Reservoir, Did I understand it right ?
post Aug 30 2012, 02:53
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Ok, so I've read some posts and learned a bit about the principles, but, something is still not clear...

- In V0, there is room for frames to go higher than 320kbps while sparing these bits on the low bitrate frames? (It can go a bit higher than 320 kbps limit)

- In 320 CBR, that doesn't happen, because the frame is literally stuck and can't got higher than 320 kbps, and thus it wastes on the frames that were with low bitrate. (It cannot go higher the 320kbps limit)

Is it still true that VBR would not be so consistent/precise as 320 in terms of choosing the right bitrate for a particular frame: eg: a frame needs 256 k but it "guesses" and calculates 250 k and then it was not truly consistent?

Thanks for answers.

This post has been edited by krafty: Aug 30 2012, 02:55
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post Aug 30 2012, 09:04
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Bit reservoir is used with CBR (especially CBR 320), ABR, VBR.
Bit reservoir is the data space within a frame which is not used for audio data of the current frame. It can be used for audio data storage of the subsequent frame(s) - within specific limitations. This way bitrate can locally be roughly 50% higher than 320 kbps. It's all about frame data usage and is not restricted by CBR 320 or any other encoding mode.

As for choosing the "right" bitrate: The encoding machinery doesn't know the "right" bitrate, it just tries to do it right. The quality measurement of VBR and CBR is different, and for low to moderate quality levels VBR should be better in the overall view as long as the machinery doesn't have major flaws. For high to very high quality demands it's hard to say whether VBR or CBR is better overall. Opinion of most people probably is in favor of CBR 320 over -V0, but it was shown on HA already that -V0 can give better results than CBR 320.
And when it come to special solutions like my 3.99.5y -V0+ variant which maximizes bit reservoir, use extremely high audio data bitrate for impulses, and prevents audio data bitrate from going low (as CBR does) - and nonetheless is a VBR method -, things are becoming even more unclear as for which very high bitrate method is best in terms of quality.

This post has been edited by halb27: Aug 30 2012, 09:25

lame3100m -V1 --insane-factor 0.75
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