iphone - 我想要 iLBC 格式，但似乎只能录制 IMA4 格式的音频

Question

如何以 iLBC 格式录制音频？我从问题 # 1010343 得到了一些帮助，并实现了这段代码:

NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc] initWithCapacity:10];        
[recordSetting setValue:[NSNumber numberWithInt:kAudioFormatAppleIMA4] forKey:AVFormatIDKey];
//  [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatMPEG4AAC] forKey:AVFormatIDKey];  //  doesn't work:  no error, but no sound
//  [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatiLBC] forKey:AVFormatIDKey];  //  doesn't work:  no error, but not sound
[recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey];
[recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
[recordSetting setObject:[NSNumber numberWithInt:12800] forKey:AVEncoderBitRateKey];
[recordSetting setObject:[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
[recordSetting setObject:[NSNumber numberWithInt: AVAudioQualityHigh] forKey: AVEncoderAudioQualityKey];
recorder = [[AVAudioRecorder alloc] initWithURL:audioFile settings:recordSetting error: &avError ];
[recorder setDelegate:self];
[recorder recordForDuration:(NSTimeInterval) secLeft];
[recorder record];

和上面一样，它工作正常。好录音。轻松播放。您注意到其他格式被注释掉了。如果我尝试其中任何一个，我什么也得不到。我想要更小的文件，根据问题 # 7279643 ，它提供了这个有值(value)的信息:

Here are the results for few encoding supported by iPhone:
Size of audio file of duration 10 sec.
   kAudioFormatMPEG4AAC :      164 kB
   kAudioFormatAppleLossless : 430 kB
   kAudioFormatAppleIMA4 :     475 kB
   kAudioFormatULaw :          889 kB
   kAudioFormatALaw :          889 KB

我应该可以在 iLBC 中录制。但如果我尝试，我什么也得不到。当我使用 IMA4 格式以外的格式时，是否需要在录制或播放中更改其他内容？

这是我的播放代码:

NSError     *avError;
AVAudioSession *audioSession = [AVAudioSession sharedInstance];
[audioSession setCategory:AVAudioSessionCategoryPlayback error:&avError];
[audioSession setActive:YES error:&avError];
if( !avError ) {
    if( [audioPlayer isPlaying] ) {
        [audioPlayer stop ];
    }
    while( ![audioPlayer isPlaying] ) {
        AVAudioPlayer *player = [[AVAudioPlayer alloc] initWithContentsOfURL:audioFile  error:nil];
        self.audioPlayer = player;
        self.audioPlayer.numberOfLoops = 0;
        [audioPlayer prepareToPlay];
        [audioPlayer play];
    }
} else {
    NSLog(@"Playback Error: %@", avError );
}

Answer 1

通过删除修复它:

[recordSetting setValue:[NSNumber numberWithFloat:44100.0]forKey:AVSampleRateKey]; 
[recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey]

我猜它们与 iLBC 默认值冲突。