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Topic: Core Audio AAC/MPEG-4 'quality' setting (Read 2803 times) previous topic - next topic
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Core Audio AAC/MPEG-4 'quality' setting

In Core Audio if you choose AAC codec and MPEG4 container you have the following options:

Extension
Quality
Bitrate
VBR

What is not clear to me is the quality setting. I made a search with google and in several related forums but the only things I came up with are these:

http://developer.apple.com/documentation/M.../reference.html a very technical description with doesn't really state more than "if you choose 'Maximum' it will take longer than if you choose 'Minimum'"
http://www.hydrogenaudio.org/forums/index....showtopic=63863 I'm not sure if he mixes up kAudioCodecBitRateControlMode_VariableConstrained with kAudioCodecPropertyQualitySetting here
http://forums.sbooth.org/viewtopic.php?t=3...quality+setting only references the first one

So what does the 'quality' setting actually do?

Michael

Core Audio AAC/MPEG-4 'quality' setting

Reply #1 –
Quality sets the encoder precision. It does neither generally increase or decrease bit rate nor change the output bitstream's format. The default medium setting should be fine, but maximum can lead to better results in theory (it has never been proven by blind testing). iTunes normally uses the faster medium setting, only the iTunes Plus mode uses maximum quality.
 

Core Audio AAC/MPEG-4 'quality' setting

Reply #2 –
Here's a bit another bit of Apple documentation:

quality setting