Has the iTunes AAC encoder changed recently?, specifically between version 7.0.2.16 and the current 7.3.4 Options

[STL]

I want to know if the iTunes AAC encoder has changed since 7.0.2.16? If so, are the changes -- overall -- for the good or bad? I don't want to upgrade if the current version of the encoder has some bad tweaks in it.

Moderation: Fixed typo in topic. ACC -> AAC. To help future searches.

This post has been edited by JensRex: Nov 6 2007, 19:47

[skuo]

A new AAC-LC codec is available in the new Mac OS X 10.5 (code named as Leopard) which will be released in Oct. 26. It has some significant sound quality improvement and bitrate mode enhancement. Since iTunes and QT use the AAC codec built natively in the OS X, these enhancements will be reflected in these Apple applications as well (doesn't matter you have upgraded these individual applications or not). You can also use the following commandline tools available in the OS X 10.5 to access the codec:
$> afconvert - perform various audio file conversions, including AAC encoding and decoding.
$> afplay - play back an audio file (compressed or uncompressed).
$> afinfo - display information about an audio file.

This post has been edited by skuo: Nov 14 2007, 23:45

[Busemann]

A new AAC-LC codec is available in the new Mac OS X 1.5 (code named as Leopard) which will be released in Oct. 26. It has some significant sound quality improvement and bitrate mode enhancement. Since iTunes and QT use the AAC codec built natively in the OS X, these enhancements will be reflected in these Apple applications as well (doesn't matter you have upgraded these individual applications or not). You can also use the following commandline tools available in the OS X 1.5 to access the codec:
$> afconvert - perform various audio file conversions, including AAC encoding and decoding.
$> afplay - play back an audio file (compressed or uncompressed).
$> afinfo - display information about an audio file.

I just received my copy of 10.5 and a nice new feature is that iTunes lists the actual bitrate of AAC VBR files, albeit only ones encoded in Leopard. The encoder is indeed updated as well since the bitrates are completely different on some test encodes I did compared to the previous version. I haven't had time to do abx tests yet though.

FLAC doesn't seem to be supported.

[skuo]

The encoder is indeed updated as well since the bitrates are completely different on some test encodes I did compared to the previous version. I haven't had time to do abx tests yet though.

You should hear the sound quality improvement as well.

Although Apple applications offer a convenient way to access Apple AAC codecs, for Mac users, the best way to access the full functionality of the codecs is through those af* commandline tools (afconvert, afinfo, afplay). All other applications only use a subset of it. For instance, iTunes only uses ABR and VBR_Constraint encoding modes. QuickTime is better, it accesses most of the feature set, but it can only encodes to a set of pre-determined discrete bitrates (afconvert can encode to any arbitrary bitrate as long as it is within the supported bitrate range).

FLAC doesn't seem to be supported.

No, it's not in the supported codecs for consumers. It's only supported through SDK.
HE-AAC is not supported yet as many have figured.

[Busemann]

Although Apple applications offer a convenient way to access Apple AAC codecs, for Mac users, the best way to access the full functionality of the codecs is through those af* commandline tools (afconvert, afinfo, afplay). All other applications only use a subset of it. For instance, iTunes only uses ABR and VBR_Constraint encoding modes. QuickTime is better, it accesses most of the feature set, but it can only encodes to a set of pre-determined discrete bitrates (afconvert can encode to any arbitrary bitrate as long as it is within the supported bitrate range).

I played around with the command line to access the true VBR mode in order to get high quality VBR files, but I'm not sure if I got it right;

afconvert -f m4af -d aac -s 3 -q 127

This setting produced vbr files with a fairly low bitrate (80-140kbps), and the bitrate option (-b) didn't make any difference.. Is there a way to make the true vbr mode aim for transparency and higher bitrate files?