Audio Level Metering with iPod Application

Subject: Audio Level Metering with iPod Application
From: abcd abcd <email@hidden>
Date: Fri, 26 Jun 2009 16:58:13 -0400
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Hi,

I am creating an iPhone application that is to run while music from the iPod application is playing. I need information about the music currently being played by the iPod application. Specifically, at a given time, I need to know the volume at different frequency bands and the peak volume of the audio. If this is not possible, the average power and peak power of the audio would be useful.

For example, while playing a song using AVAudioPlayer I can use the averagePowerForChannel: and peakPowerForChannel: methods to retrieve this information. Unfortunately, it is not so simple for audio coming from an external application (the iPod).

I considered using MPMusicPlayerController to find out the song currently being played. Then, I thought, I could play the same song in AVAudioPlayer to access the information I need. However, I cannot play a song from the iPod library using AVAudioPlayer and, as a result, this idea does not work.

I noticed that AVAudioRecorder supports audio level metering. Therefore, I considered using this by changing the input source to be the audio output of the iPhone. Because I do not know how to do this, this idea also does not work.

I would really appreciate any advice for how I can retrieve the information I need from a song playing in the iPod application.

Thank you in advance!

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