I haven't used it myself, but Apple's avTouch iPhone sample has bar graphs powered by AVAudioPlayer, and you can easily check to see how they do it.
mahboudz
2009-11-20 00:16:30
A:
I know this sample and the key difference is that they are _playing_ the audio file. I don't need to play it. I need to investigate an arbitrary part of the file at an arbitrary moment of time without actually playing it. And to build a graph that would visualize that characteristics.
Aleks N.
2009-11-20 01:41:19
Ahhhh... You'll have to read the data yourself and find the levels for selected periods. And since the file is not decompressed, you will have to decode it, or use other frameworks to get to the PCM data. I understand that ExtAudio, AudioQueue, and Remote IO AudioUnit would be areas for you to look into. I'm still learning myself.
mahboudz
2009-11-20 08:28:25
>>And since the file is not decompressed, you will have to decode it --> Please, don't reply if you don't know the answer. There is no difference in reading compressed or raw data. SDK is handling all this. Thus you're just misleading people who will reading you afterwards.
Aleks N.
2009-11-20 13:54:06
Are you saying that if you looked at the contents of the file whose URL you are passing to AVAudioPlayer, it would look the same whether it was compressed or decompressed? Then why bother using ExtAudioFile?
mahboudz
2009-11-20 19:28:23
A:
I don't think you can use AVAudioPlayer based on your constraints. Even if you could get it to "start" without actually playing the sound file, it would only help you build a graph as fast as the audio file would stream. What you're talking about is doing static analysis of the sound, which will require a much different approach. You'll need to read in the file yourself and parse it manually. I don't think there's a quick solution using anything in the SDK.
Shaggy Frog
2009-11-20 02:59:19
A:
Ok guys, seems I'm going to answer my own question again: http://www.supermegaultragroovy.com/blog/2009/10/06/drawing-waveforms/ No a lot of concretics, but at least you will know what Apple docs to read.
Aleks N.
2009-11-20 11:48:53
I know this is just under a year old now, but in your original post you did say you were going to post an open-source component. I read your blog post but didn't see anything downloadable. Have I missed something or did you change your mind?
Tom Irving
2010-09-25 17:53:53
I didn't change my mind, but I simply never got a chance to do it. Write an email to me with your needs, and probably I'll be able to help you.
Aleks N.
2010-09-25 18:45:14