iphone - iPhone 4sでm4aファイルが再生されない

Question

オーディオ ファイルを m4a 形式で録音するためのコードを実装しました。ipod では正常に動作しますが、iphone 4s では再生できません。

私のコードは次のとおりです。

-(IBAction)recordAudio:(id)sender
{

    NSDictionary * recordSetting = [[NSMutableDictionary alloc] init];
    [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatAppleLossless] forKey:AVFormatIDKey];
    [recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey];
    [recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
    [recordSetting setValue:[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
    [recordSetting setValue:[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsBigEndianKey];
    [recordSetting setValue:[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsFloatKey];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *documentsDirectory = [paths objectAtIndex:0];

    NSString *task = [[NSUserDefaults standardUserDefaults]valueForKey:@"accidenttask"];


  recordPath= [[NSString stringWithFormat:@"%@/%d.m4a",DOCUMENTS_FOLDER,a_id]retain];

 url=[NSURL fileURLWithPath:recordPath];

    NSError *err = nil;
    if([recorder isRecording])
    {
        [recorder stop];
        recorder = nil;
    }
    recorder = [[ AVAudioRecorder alloc] initWithURL:url settings:recordSetting error:&err];

    if(err)
        NSLog(@"ERROR : %@", err);
    BOOL st = [recorder prepareToRecord];
    if(!st){
        NSLog(@"Failed");
    }
    recorder.meteringEnabled = YES;
    BOOL status = [recorder record];
    if(!status)
        NSLog(@"Failed");


}


-(IBAction)stop:(id)sender
{
        [stopButton setHidden:YES];
    [playButton setHidden:NO];
    [recordButton setHidden:NO];
        [recorder stop];


}


-(IBAction)playAudio:(id)sender
{
    [recorder stop];
    if (!recorder.recording)
    {

        NSError *error;

            recordPath= [[NSString stringWithFormat:@"%@/%d.m4a",DOCUMENTS_FOLDER,a_id]retain];
            NSString *filename=[[filearry objectAtIndex:0]valueForKey:@"audiofile_path"];

            url=[ NSURL fileURLWithPath:filename];
            audioPlayer = [[AVAudioPlayer alloc]  initWithContentsOfURL:[NSURL fileURLWithPath:filename] error:nil]; 
            [audioPlayer setVolume:1.0];
            [audioPlayer prepareToPlay];
            [audioPlayer play];

        }
}

何が問題になる可能性がありますか?