ios CAF音频转换为MP3

 

Url:http://blog.csdn.net/ysy441088327/article/details/7392842#reply

 为了达到 iPhone 与 Android 实现音频互通. 那么Mp3格式的音频文件再好不过了.

至于能够转换成Amr 是最好,10秒 的 一个Amr文件 只有5K左右的大小. 非常适合移动设备的数据传输

 

这里主要用到lame,一款非常棒的Mp3音频编码器.   

那么在转换之前呢? 就需要先录制好音频文件,使用 AVAudioRecorder 进行音频录制之前,进行如下参数设置:

- (void)initialRecord

{

    //录音权限设置，IOS7必须设置，得到AVAudioSession单例对象

    AVAudioSession *audioSession = [AVAudioSession sharedInstance];

    //设置类别,此处只支持支持录音

    [audioSession setCategory:AVAudioSessionCategoryRecord error:nil];

    //启动音频会话管理,此时会阻断后台音乐的播放

    [audioSession setActive:YES error:nil];

    //录音参数设置设置

    NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc]init];

    //设置录音格式  AVFormatIDKey==kAudioFormatLinearPCM

//    [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatMPEG4AAC] forKey:AVFormatIDKey];

    //caf的录制格式

   [recordSetting setValue:[NSNumber numberWithInt:kAudioFormatLinearPCM] forKey:AVFormatIDKey];

    

    //设置录音采样率(Hz) 如：AVSampleRateKey==8000/44100/96000（影响音频的质量）//acc的采样频率

//    [recordSetting setValue:[NSNumber numberWithFloat:44100] forKey:AVSampleRateKey];

    

    [recordSetting setValue:[NSNumber numberWithFloat:11025.0] forKey:AVSampleRateKey];

    //录音通道数  1 或 2 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

    [recordSetting setValue:[NSNumber numberWithInt:2] forKey:AVNumberOfChannelsKey];

    //线性采样位数  8、16、24、32

    [recordSetting setValue:[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];

    //录音的质量

//    [recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityHigh] forKey:AVEncoderAudioQualityKey];

    [recordSetting setValue:[NSNumber numberWithInt:AVAudioQualityMin] forKey:AVEncoderAudioQualityKey];

    

    //录音文件保存的URL

    CFUUIDRef cfuuid = CFUUIDCreate(kCFAllocatorDefault);

    NSString *cfuuidString = (NSString*)CFBridgingRelease(CFUUIDCreateString(kCFAllocatorDefault, cfuuid));

    NSString * filename = [NSString stringWithFormat:@"%@.caf",cfuuidString];

    NSString *audioRecordFilePath = AUDIORECORDFILEPATH(filename);

    lastaudioRecordFilePath = audioRecordFilePath;

    

    //判断目录是否存在不存在则创建

    NSString *audioRecordDirectories = [audioRecordFilePath stringByDeletingLastPathComponent];

    NSFileManager *fileManager=[NSFileManager defaultManager];

    if (![fileManager fileExistsAtPath:audioRecordDirectories]) {

        [fileManager createDirectoryAtPath:audioRecordDirectories withIntermediateDirectories:YES attributes:nil error:nil];

    }

    NSURL *url = [NSURL fileURLWithPath:audioRecordFilePath];

    NSError *error=nil;

    //初始化AVAudioRecorder

    _recorder = [[AVAudioRecorder alloc]initWithURL:url settings:recordSetting error:&error];

    if (error != nil) {

        //NSLog(@"初始化录音Error: %@",error);

    }else{

        if ([_recorder prepareToRecord]) {

            //录音最长时间

            [_recorder recordForDuration:self.recorderDuration-1];

            _recorder.delegate=self;

            [_recorder record];

            

            //开启音量检测

            _recorder.meteringEnabled = YES;

            //开启定时器，音量监测

            _timer=[NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(volumeMeters:) userInfo:nil repeats:YES];

        }

    }

}

　　 

通过上面的参数所录制的音频文件体积非常大,不过不要担心,这只是第一步,只要成功转换成Mp3以后,可以保证文件体积每秒在4K左右.^^

另外一点,除非你时间多,那么没必要去尝试设置其他种类的参数再用来转换,因为作者我就试了不少,反正只有上面的参数才能保证,音质的完整和流畅.

 

 

下面介绍 lame 静态库 使用流程 主要有两个核心文件,使用很简单:

需要加入 lame.h

#include "lame.h"  

 

//转编码为 mp3
- (void)audio_PCMtoMP3:(NSString *)cafFilePath andMP3FilePath:(NSString *)mp3FilePath
{
    NSFileManager* fileManager=[NSFileManager defaultManager];
    if([fileManager removeItemAtPath:mp3FilePath error:nil]) {
        NSLog(@"删除");
    }
    
    @try {
        int read, write;
        
        FILE *pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb");  //source 被转换的音频文件位置

        if(pcm == NULL) {
            NSLog(@"file not found");
        } else {
            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 {
        NSLog(@"MP3生成成功");
    }
}

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