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iTunes Store AAC Encoder Version Used
wottha
post Sep 9 2013, 20:28
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Is there a way to determine the version of the AAC encoder used to make any particular AAC purchased from the iTunes store?
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db1989
post Sep 9 2013, 23:08
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Are you asking about the encoder itself or simply which iteration was used for any one file?

Just in case it was the former: All files sold are encoded as iTunes Plus using Apple’s own encoder, technically a part of QuickTime. Users here have reverse-engineered this to determine the relevant parameters in the past and reported iTunes Plus to be equivalent to constrained VBR (CVBR) at 256 kbps and with the maximal quality setting. If anything has been updated, you should be able to find that by searching. You could also check the technical discussion in other threads, again likely to be found through searching, such as the one about QAAC, a frontend for QuickTime’s AAC encoder.

As for the latter, I imagine any program that can display metadata/technical info from MP4/AAC files could tell you the version number, assuming Apple include it and do so in a standard form and not some proprietary extension; still, if the latter, there will be other programs that can still find it. Perhaps another reader can recommend something specific, but to start, you could check the file with something like MP3tag or foobar2000.
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marc2003
post Sep 9 2013, 23:36
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i just tested my most recent itunes purchase with foobar/mp3tag and they don't show anything. ditto using the Get info dialog within itunes. lastly, i also tried the atomicparsley command line tool and again, nothing.
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db1989
post Sep 9 2013, 23:46
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Thanks for the report. I guess Apple store it either in a proprietary form or not at all. Could someone with an iTunes Plus file at hand have a look using a hex editor and see whether the number is embedded anywhere else in the file? Unless the format or absence of the version has already been confirmed elsewhere, of course.
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jkauff
post Sep 10 2013, 00:00
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I just looked at an iTunes Plus file with MediaInfo, and there's no version information. There's a line that reports "Codec ID=40" if that means anything to you.
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testyou
post Sep 10 2013, 00:27
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This FAQ doesn't provide technical information, but it says:
QUOTE
Why is iTunes Plus format available for certain music, but not all?
The reason that certain music and music videos are not offered in our DRM-free, highest quality audio format is because they have not been provided in iTunes Plus format from the music label.

I had previously thought that only "Mastered for iTunes" had to be supplied as such from the label, but it looks like this has to be too.

The qaac Wiki describes iTunes Plus as the settings:
QUOTE
iTunes Plus(256k) -v256 -q2

which is from the discussion threads linked by db1989. It uses Core Audio framework for encoding.

This post has been edited by testyou: Sep 10 2013, 00:40
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binaryhermit
post Sep 10 2013, 00:33
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My understanding is that they've stopped selling all non-plus iTunes music store files (Wikipedia says in April 2009) and that FAQ is therefore somewhat out of date.
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db1989
post Sep 10 2013, 02:36
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Correct. For audio, Plus is the only format offered.

Edit: still hoping for someone to have a look in a hex editor to see whether a version string is embedded somewhere. I would do it myself tomorrow, but I seem to have misplaced my iPod. :/

This post has been edited by db1989: Sep 10 2013, 02:45
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marc2003
post Sep 10 2013, 06:25
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who knows where to even begin looking in a hex editor? tongue.gif

itunes itself does report an Encoded with string if you use a tool like QAAC to create your own m4a files. this also shows under the technical information in both foobar and mp3tag so i presume it is some kind of standard? i'm not sure if there is going to be anything found deeper inside an itunes store file???

qaac generated file:



this is an itunes store file:







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db1989
post Sep 10 2013, 12:05
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QAAC probably adds that itself to match other encoders.

Anyway, Apple might have their encoding pipeline set not to write the information or to remove it before uploading to the Store.
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nu774
post Sep 10 2013, 16:23
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QUOTE (db1989 @ Sep 10 2013, 20:05) *
QAAC probably adds that itself to match other encoders.

Yes.

QUOTE
Anyway, Apple might have their encoding pipeline set not to write the information or to remove it before uploading to the Store.

Maybe they are using afconvert and it doesn't write "com.apple.iTunes:Encoding Params" or tool tag like iTunes, but I don't know.
As for iTunes, some information such as version of AAC encoder component are stored into "com.apple.iTunes:Encoding Params" in binary form, but I don't know if somebody actually looks at it.
As far as I know, iTunes is using it only to distinguish VBR files on the property dialog.

Version of encoder component is currently 1.7.1, but I don't think it's quite useful a number. It hasn't been updated recently even known bug of encoder has been fixed (at least from CoreAudioToolbox 7.9.7.3), and at the time of CoreAudioToolbox 7.9.3.0 it was "1.7.2" (so version number has decreased since then).
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wottha
post Sep 10 2013, 21:09
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Thanks everyone. I really appreciate the information and suggestions. You all got further than I did. Maybe it's just not there. I have found ISRC with a hex editor because Apple doesn't use the ID3 ISRC field. But search keywords I've tried for aac encoder version (tool, codec), I can't find anything. Thanks all for the help.

This post has been edited by wottha: Sep 10 2013, 22:06
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