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aac encoding differences

post #1 of 2
3/6/11 at 2:11pm
Thread Starter 

i was bored and decided to import a cd multiple times in different formats/bitrates just to see the size differences, and how small they are (or aren't). when i imported a song (with a hidden track following a few minutes or so of silence - ...but home is nowhere by afi) the aac 256 vbr was 29mb, and the aac 256 cbr was 27mb - both with artwork embedded. what causes this? just curious. can the aac 256 vbr go above 256, or only below?

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post #2 of 2
3/6/11 at 2:34pm

You don't state what encoder you are using.

 

Strictly speaking, frequency domain lossy coding is never CBR, as blocks have different sizes, as well as the bits each block takes up vary a lot. When you select a CBR mode, the encoder is simply more strict in its bit allocation versus time than in VBR, but deep down, it's always VBR. Yes, usually they both can go over the target average bitrate.

 

In this case the bit allocation algorithm ended up choosing "high-ish" bitrates throughout, and ended up slightly over the target average 256 kb/s. In CBR mode, bit allocation is more tightly controlled, and as such the deviation was smaller.

 

 

I realize this might read like gibberish but... You asked tongue.gif


Edited by Wildstar - 3/6/11 at 2:39pm
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