Apple AAC quality

[moneymatt4life]

Hello, I attempted to see if this was mentioned somewhere but perhaps the wording wasn't right or just not searching properly.

As I didn't see it someplace, I was wondering what is the codec quality setting for the Apple AAC encoder? There are no encoder configuration options aside from bitrate mode and profile like there are with the other codecs, so no way to really tell what the quality setting is. I thought afconvert defaulted to the medium quality of -q 64 if not specified, would that also be the case here?
If it's not already in the highest quality range, -q 96-127 are the same from what I saw even though Apple specifies -q 127 for it's digital master encoding, is it planned to let users choose what the encoding quality is otherwise or no?

[PeterP]

Re: Apple AAC quality

The quality slider is directly mapped to afconvert -u vbrq values.
For an example, LC AAC with Quality of 100 calls Apple afconvert like this:

/usr/bin/afconvert -f mp4f -d aac -u vbrq 100

If you'd like to specify other afconvert options, please tell me what exact ones you're interested in and I'll add them for the next dBpoweramp update.

[moneymatt4life]

Re: Apple AAC quality

Right, there are two quality values one can specify, the vbrq value and codec quality value. Similarly to how LAME mp3 has both a -V value and -q value. In the case of afconvert, it defaults to 64 for both whichever isn't specified from what I see.

so my typical afconvert string would be

afconvert -d aac -f m4a -ue vbrq 82 -q 127 file.flac

just as a quick, not completely thorough, test for TVBR encoding

afconvert -d aac -f m4af -ue vbrq 64 testfile.flac
Size: 6,352,278 bytes

afconvert -d aac -f m4af -ue vbrq 64 -q 96 testfile.flac
Size: 6,407,777 bytes

afconvert -d aac -f m4af -s 3 testfile.flac
Size: 6,352,278 bytes

afconvert -d aac -f m4af -s 3 -q 64 testfile.flac
Size: 6,352,278 bytes

afconvert -d aac -f m4af -s 3 -q 96 testfile.flac
Size: 6,407,777 bytes

afconvert -d aac -f m4af -s 3 -q 127 testfile.flac
Size: 6,407,777 bytes

The Hydrogenaudio page says that the even though the -q value can be anything up to 127, it says it gets rounded to 32, 64, or 96.
So that's where I was asking, as the user cannot specify the encoder quality value, what dBpoweramp specifies the quality value as or if it's defaulted to -q 64 since dBpoweramp doesn't specify that value.

The current quality slider that relates to the bitrate range is fine as is, even though that too only has a set number of fixed values that afconvert rounds to as well.

So if the option is open to allow users to select what encoding quality value they'd like to use, maybe a dropdown to the left of the profile selector that one could select either Low, Medium, or High quality for the encoding. So in regards to the afconvert value would be, -q 32 (Low), -q 64 (Medium), or -q 96 (High). Not sure -q 0 (Minimum) or -q 127 (Maximum) would really be needed as it should get rounded as well, but just for completeness sake maybe.

[PeterP]

Re: Apple AAC quality

Implemented:

https://www.dbpoweramp.com/beta/DMC-2023-11-21.dmg

Added -q slider (0..127). Not sure about restricting to just 3 modes, will check some more how different modes behave.
Highest quality mode has been made the default as it's still very fast on current hardware, not sure what uses the lower modes might have when encoding on a modern-day Mac.

[PeterP]

Re: Apple AAC quality

Amended:

https://www.dbpoweramp.com/beta/DMC-2023-11-22.dmg

If there are only 3 actual modes, a dropdown list makes more sense. Also better to use -q 127 for max than some lower value - in case future version of the encoder adds more distinct modes, you can still access the highest quality one.