iOS音频caf转mp3

导入lame
gitbub地址：
https://github.com/hedgehogIda/caf-mp3

在录制caf文件时，需要使用双通道，否则在转换为MP3格式时，声音不对。caf录制端的设置为：
 
NSMutableDictionary * recordSetting = [NSMutableDictionary dictionary];
 
[recordSetting setValue :[NSNumber numberWithInt:kAudioFormatLinearPCM] forKey:AVFormatIDKey];//
[recordSetting setValue:[NSNumber numberWithFloat:8000.0] forKey:AVSampleRateKey];//采样率
[recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];//声音通道，这里必须为双通道
 [recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityLow] forKey:AVEncoderAudioQualityKey];//音频质量
在转换mp3端的代码为:
 NSString *cafFilePath = destPath;    //caf文件路径
 NSString *mp3FilePath = mp3FilePath;//存储mp3文件的路径

 @try {
        int read, write;
        
        FILE *pcm = fopen([destPath cStringUsingEncoding:1], "rb");  //source 被转换的音频文件位置
        fseek(pcm, 4*1024, SEEK_CUR);                                   //skip file header
        FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb");  //output 输出生成的Mp3文件位置
        
        const int PCM_SIZE = 8192;
        const int MP3_SIZE = 8192;
        short int pcm_buffer[PCM_SIZE*2];
        unsigned char mp3_buffer[MP3_SIZE];
        
        lame_t lame = lame_init();
        lame_set_in_samplerate(lame, 11025.0);
        lame_set_VBR(lame, vbr_default);
        lame_init_params(lame);
        
        do {
            read = fread(pcm_buffer, 2*sizeof(short int), PCM_SIZE, pcm);
            if (read == 0)
                write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
            else
                write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);
            
            fwrite(mp3_buffer, write, 1, mp3);
            
        } while (read != 0);
        
        lame_close(lame);
        fclose(mp3);
        fclose(pcm);
    }
    @catch (NSException *exception) {
        NSLog(@"%@",[exception description]);
    }
    @finally {
        
    }

补充

先说明一点，默认AVAudioRecorder录制后的格式是.caf，而大部分的播放器都是不支持这个格式的，下面一段设置是可以让录制格式是wav的格式kAudioFormatLinearPCM],AVFormatIDKey

#录制
NSDictionary *recordSetting = [[NSDictionary alloc] initWithObjectsAndKeys:

[NSNumber numberWithFloat: 44100.0],AVSampleRateKey, //采样率

[NSNumber numberWithInt: kAudioFormatLinearPCM],AVFormatIDKey,

 [NSNumber numberWithInt:16],AVLinearPCMBitDepthKey,//采样位数
 默认 16

[NSNumber numberWithInt: 2], AVNumberOfChannelsKey,//通道的数目

[NSNumber numberWithBool:NO],AVLinearPCMIsBigEndianKey,//大端还是小端
 是内存的组织方式

[NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,nil];//采样信号是整数还是浮点数

 _recordedFile = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingString:@"RecordedFile"]];//文件存储位置
 NSError* error;
_recorder = [[AVAudioRecorder alloc] initWithURL:_recordedFile settings:settings error:&error];//设置AVAudioRecorder

#转为Mp3
- (void) toMp3
{
    NSString *cafFilePath =[NSTemporaryDirectory() stringByAppendingString:@"RecordedFile"];
    
    NSString *mp3FileName = @"Mp3File";
    mp3FileName = [mp3FileName stringByAppendingString:@".mp3"];
    NSString *mp3FilePath = [[NSHomeDirectory() stringByAppendingFormat:@"/Documents/"] stringByAppendingPathComponent:mp3FileName];
    
    @try {
        int read, write;
        
        FILE *pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb");  //source
        fseek(pcm, 4*1024, SEEK_CUR);                                   //skip file header
        FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb");  //output
        
        const int PCM_SIZE = 8192;
        const int MP3_SIZE = 8192;
        short int pcm_buffer[PCM_SIZE*2];
        unsigned char mp3_buffer[MP3_SIZE];
        
        lame_t lame = lame_init();
        lame_set_in_samplerate(lame, _sampleRate);
        lame_set_VBR(lame, vbr_default);
        lame_init_params(lame);
        
        do {
            read = fread(pcm_buffer, 2*sizeof(short int), PCM_SIZE, pcm);
            if (read == 0)
                write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);
            else
                write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);
            
            fwrite(mp3_buffer, write, 1, mp3);
            
        } while (read != 0);
        
        lame_close(lame);
        fclose(mp3);
        fclose(pcm);
    }
    @catch (NSException *exception) {
        NSLog(@"%@",[exception description]);
    }
    @finally {
        [self performSelectorOnMainThread:@selector(convertMp3Finish)
                               withObject:nil
                            waitUntilDone:YES];
    }
}