Best API for instant voice playback on iPhone?

Question

What I am trying to do:

• iPhone keep monitoring the voice input channel
• once the user speaks (recording sound volume > certain level)
• iPhone starts recording
• once the use stop speaking (recording volume silence for one second)
• iPhone plays back the recording

Which iPhone API or sample code should I look into? Thanks!

Answer 1

What you need is AVFoundation. To use it:

1. Adding AVFoundation.framework to your project
2. conform your view controller to AVAudioRecorderDelegate, AVAudioPlayerDelegate, one for recording, another one for playing

Following piece of code is for recording:

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
NSError *err = nil;
[audioSession setCategory :AVAudioSessionCategoryPlayAndRecord error:&err];
[audioSession setActive:YES error:&err];
NSMutableDictionary *settings = [[NSMutableDictionary alloc] init];
[settings setValue: [NSNumber numberWithInt:kAudioFormatMPEGLayer3] forKey:AVFormatIDKey];
[settings setValue: [NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey]; 
[settings setValue: [NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
[settings setValue: [NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
[settings setValue: [NSNumber numberWithBool:NO] forKey:AVLinearPCMIsBigEndianKey];
[settings setValue: [NSNumber numberWithBool:NO] forKey:AVLinearPCMIsFloatKey];
NSURL *url = [NSURL fileURLWithPath: filepath];
recorder = [[ AVAudioRecorder alloc] initWithURL:url settings:settings error:&err];
[settings release];
[recorder setDelegate:self];
[recorder prepareToRecord];
[recorder record];

Addtionally, you need to implement - (void)audioRecorderDidFinishRecording:(AVAudioRecorder *) recorder successfully:(BOOL)flag to release the recorder.

Please see more details here: http://developer.apple.com/library/ios/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/00_Introduction.html#//apple_ref/doc/uid/TP40010188