“AAC” is “evil”


Few days ago, I wrote a post on which is the best audio format we should choose when developing an iPhone app. The conclusion is using IMA4, it’s the best choice if you want to record audio on the device.

Today, I was trying to use the System Sound service to play a short audio and in order to save the spaces, I chose the “AAC” format to encode my sound effects. I just thought it’s would be capable for a system sound and didn’t searched the documentation for which format is suit for System Sound. Everything went fine in the simulator. But, when I load the app into the device, and, BOOM~~, it failed to play the sound effect! My first reaction was somewhere programmatic mistake in my code, and after a careful review, I thought the reason could  be the format. So I changed the format back to IMA4, and this time, it went well!

Apparently, System sound did not support AAC format, and I could not find the appropriate document where described it. Apple just pushes us to use IMA4 and other linear PCM format to reduce the CPU and power consume. Yeah, I understand that, but please, place such kind of important information some where we can find it easily! The API documentation could be a good place.

If I am the director of the documentation team, I would promote such information and place it in a notable place! Damn it.

Why I’m angry?

Because if you using AAC for recording or System Sound, it works fine on the simulator, but will be failed on the device! If the device does not support AAC for recording and System Sound, please disable it on the simulator!


The conclusion is if you want to playback a song or something like this, you can choose AAC as your primary format for it is well supported by hardware codec, but only for this purpose please. If you want to record audio or play system sound effect, please choose IMA4, it’s is the second best format for iPhone.

“AAC” is a good compressed format, but it’s also has its cost.

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