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Why is there no vbr for aac 320kbps on itunes

post #1 of 19
Thread Starter 
I have all my music encoded at a 256kbps vbr aac but noticed that vbr is not allowed if you use 320kbps on itunes.

Why is this?
post #2 of 19
320kbps is the maximum allowed bit rate for AAC files. So you can't go above 320 kbits for any section of the song. Therefore, any variation in the encoding bit rate would necessarily drop the encoding rate below 320kbps. Therefore, it's impossible.
post #3 of 19
Quote:
Originally Posted by Clutz View Post
320kbps is the maximum allowed bit rate for AAC files. So you can't go above 320 kbits for any section of the song. Therefore, any variation in the encoding bit rate would necessarily drop the encoding rate below 320kbps. Therefore, it's impossible.
He's right. The same for MP3.
post #4 of 19
Not anymore. iTunes 9 now allows 320 kbps AAC VBR encoding.
post #5 of 19
Quote:
Originally Posted by m001 View Post
Not anymore. iTunes 9 now allows 320 kbps AAC VBR encoding.
How? Can you encode a song in iTunes 9 using 320 kbps AAC VBR and tell us what range of bitrates the file has and what bitrate the file averages out to? Are they going above 320 kbps?

I'm not going to install iTunes 9 just to test this out.
post #6 of 19
A couple of pictures of iTunes and 320kbps AAC VBR...



post #7 of 19
Ah the perils of compressed audio formats...

VBR's supposed to allow a higher bit rate... but at 320 you can't get any higher (MP3).

Or not? I just checked the wiki and found out AAC goes up to 529kbps.

Anyone have AAC on VBR going higher than 320?
post #8 of 19
It's probably just an implementation issue. I doubt there is any technical reason why most of these codecs can't be VBR at any arbitrary bit rate- it could just be that the algorithms are idiosyncratic, and so coming up with a generalized function whereby you simply specify using VBR/CBR/ABR and a bit-rate is more complicated than it's worth- so they've focused on a few specific implementations at given bit rates.
post #9 of 19
It likely means that the absolute maximum for a song will peak at 320k. Lame is listed as an average (245?) so it's simply a different way of saying the same thing.
post #10 of 19
I was always under the impression that it means that it will be around 320k at most but lower in cases where the music is very quiet and doesn't need that much sampling....

But, as I just loaded some 160kbps VBR in my Foobar2000 and watched the bottom caption as a song plays, it actually goes to over 200kbps (and as low as 130kbps). Time to read up on the theory....
post #11 of 19
in dbPoweramp with the nero codec, you can encode AAC as VBR and CBR up to 400kbps.
post #12 of 19
I seems to be broken because in itunes it says they are all 320. I was going to mention this but was too lazy. Maybe its some kind of bug?
post #13 of 19
^ Highly possible.
Cause with VBR one should assume that the bitrate varies somewhat, and not stay constant on 320kbps.
post #14 of 19
I am really gratful to you all of there for you valuable information..
post #15 of 19
I just tried to test out the VBR encoding @ 320. The VBR file was actually larger. I would think it would be smaller.
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