Question

could you point me to docs/snippets/blogs, which explain
how to record Apple lossless audio files on the iPhone, please?

I’ve inspected the audio recorder example from the Apple
Dev Center, but couldn’t figure out, which setting I have
use for lossless audio.

Regards,

Stefan

Answer 1

The iPhone OS supports recording a .caf file using a number of different compressed audio encoding formats:

Apple Lossless – kAudioFormatAppleLossless

iLBC (Internet Low Bitrate Codec) – kAudioFormatiLBC

IMA/ADPCM (aka IMA4) – kAudioFormatAppleIMA4

µLaw – kAudioFormatULaw

aLaw – kAudioFormatALaw

- (id) initWithURL: fileURL {
    NSLog (@"initializing a recorder object.");
    self = [super init];

    if (self != nil) {

        // define the audio stream basic description for the file to record into

        // record audio at the current hardware sample rate
        // make sure the audio session is active before asking for properties
        UInt32 propertySize = sizeof(audioFormat.mSampleRate);
        AudioSessionGetProperty(kAudioSessionProperty_CurrentHardwareSampleRate,
                                &propertySize,
                                &audioFormat.mSampleRate);

        audioFormat.mFormatID           = kAudioFormatAppleIMA4; // record using IMA4 codec
        audioFormat.mChannelsPerFrame   = 1;

        AudioQueueNewInput(&audioFormat, ... );

        ...

    }

    return self;
}

You’ll definitely want to read the Audio Queue Services Programming Guide