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Topic: iTunes Plus preset reverse engineered (Read 52396 times) previous topic - next topic
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iTunes Plus preset reverse engineered

Reply #25 –
Quote from: Billytheonion on
I think previous posters haven't tested enough songs. Most the time tvbr will give the exact same file size are iTunes Plus but on some occasions it does produce smaller files. As where vbr constrained 100% of the time produces the same file as iTunes Plus.


How did you come to this conclusion?  I have quite a few examples that contradict your last little bit there even when I extract the raw AAC stream without padding, tags, or anything else.  VBR constrained does not always produce the same bitrates/file sizes as the iTunes Plus setting or songs purchased from the iTunes Store.

iTunes Plus preset reverse engineered

Reply #26 –
So far, the only results backed up with evidence is the first post. I wouldn't mind seeing much of the following baseless speculation removed from the thread.

Quote from: kornchild2002 on
VBR constrained does not always produce the same bitrates/file sizes as the iTunes Plus setting or songs purchased from the iTunes Store.


You never know if the same exact encoder version has been used at Apple, so this should not be surprising. They sureley don't reencode everything for each new encoder revision. Before there is any new evidence, I think, it can still be assumed with good reason that iTunes-Plus is constrained VBR, 256 kbit/s, at max quality. It also makes sense, from a marketing viewpoint. They don't want smart-asses  starting an internet riot, when content with maximum compressibility comes out below 128 kbit/s from the TVBR encoder (which is else a big advantage). CVBR never departs far from the set rate so people can have the feeling that they got what they've paid for with iTunes plus.

iTunes Plus preset reverse engineered

Reply #27 –
Using Quicktime 7.6.8, iTune 10.0.68, and latest qtaacenc and I get different results on windows.  Using iTunes Plus setting, a classic track ends up according to Foobar2000 with a 15.3MB file with Bitrate at 259kbit.  Using Foobar2000 and qtaacenc with --tvbr 110 --highest I get a 12.9MB file with bitrate 217.  Now if I encode using --cvbr 256 --highest I get a 15.4MB file with bitrate 259.

SO...  it appears, at least on Windows, iTunes 10 is still using constrained VBR not true VBR.  I wish foobar was better at recognizing CD's as good as iTunes was. 

I was wondering what the point of CVBR was anyway.  It is once again Apple trying to be Consumer friendly. Consumers would think a TVBR file with 224kbit avg bitrate is inferior to CVBR 255kbit when it isn't.  It is just a way of keeping the bitrates consistent for simplicity sake.  In my opinion.

Per the Variable Bitrate Wikipedia entry:

"Some encoders also allow the user to specify a maximum allowed bitrate or maximum quality value. This is sometimes called Constrained Variable Bitrate (CVBR), and is typically applied to ABR algorithms.
The disadvantage of single pass ABR encoding (with or without CVBR) is the opposite of fixed quantizer VBR — the size of the output is known ahead of time, but the resulting quality is unknown, although still better than CBR.[14] Specifying a higher average or maximum may simply make the file bigger with no discernible quality effect"

iTunes Plus preset reverse engineered

Reply #28 –
Consultant as far as I've seen there is absolutely no difference from a quality point of view between 7.6.7 and 7.6.8; all the files I've tested (both CVBR and TVBR) are identical and bit-compared, 7.6.8 is just a security update.

For the CVBR TVBR thing, well like I said earlier a lot of songs result identical with TVBR 110 (or 113 is the same thing) and CVBR 256 while others not, CVBR uses more bits (or should I say "wastes"? lol).

iTunes Plus preset reverse engineered

Reply #29 –
Consultant i tested a bit more and you were right, the latest update definitely deals also with AAC encoder; It will surely come soon for Mac too. I noticed that many songs have different bitrates and even smaller file sizes.