ios CAF音頻轉換爲MP3

 

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

 爲了達到 iPhone 與 Android 實現音頻互通. 那麼Mp3格式的音頻文件再好不過了.

至於可以轉換成Amr 是最好,10秒 的 一個Amr文件 只有5K左右的大小. 很是適合移動設備的數據傳輸

 

這裏主要用到lame,一款很是棒的Mp3音頻編碼器.   

那麼在轉換以前呢? 就須要先錄製好音頻文件,使用 AVAudioRecorder 進行音頻錄製以前,進行以下參數設置:

- (void)initialRecord

{

    //錄音權限設置，IOS7必須設置，獲得AVAudioSession單例對象

    AVAudioSession *audioSession = [AVAudioSession sharedInstance];

    //設置類別,此處只支持支持錄音

    [audioSession setCategory:AVAudioSessionCategoryRecord error:nil];

    //啓動音頻會話管理,此時會阻斷後臺音樂的播放

    [audioSession setActive:YES error:nil];

    //錄音參數設置設置

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

    //設置錄音格式  AVFormatIDKey==kAudioFormatLinearPCM

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

    //caf的錄製格式

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

    

    //設置錄音採樣率(Hz) 如：AVSampleRateKey==8000/44100/96000（影響音頻的質量）//acc的採樣頻率

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

    

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

    //錄音通道數  1 或 2 在錄製caf文件時，須要使用雙通道，不然在轉換爲MP3格式時，聲音不對

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

    //線性採樣位數  八、1六、2四、32

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

    //錄音的質量

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

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

    

    //錄音文件保存的URL

    CFUUIDRef cfuuid = CFUUIDCreate(kCFAllocatorDefault);

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

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

    NSString *audioRecordFilePath = AUDIORECORDFILEPATH(filename);

    lastaudioRecordFilePath = audioRecordFilePath;

    

    //判斷目錄是否存在不存在則建立

    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(@"初始化錄音Error: %@",error);

    }else{

        if ([_recorder prepareToRecord]) {

            //錄音最長時間

            [_recorder recordForDuration:self.recorderDuration-1];

            _recorder.delegate=self;

            [_recorder record];

            

            //開啓音量檢測

            _recorder.meteringEnabled = YES;

            //開啓定時器，音量監測

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

        }

    }

}

　　 

經過上面的參數所錄製的音頻文件體積很是大,不過不要擔憂,這只是第一步,只要成功轉換成Mp3之後,能夠保證文件體積每秒在4K左右.^^

另一點,除非你時間多,那麼不必去嘗試設置其餘種類的參數再用來轉換,由於做者我就試了很多,反正只有上面的參數才能保證,音質的完整和流暢.

 

 

下面介紹 lame 靜態庫 使用流程 主要有兩個核心文件,使用很簡單:

須要加入 lame.h

#include "lame.h"  

 

//轉編碼爲 mp3
- (void)audio_PCMtoMP3:(NSString *)cafFilePath andMP3FilePath:(NSString *)mp3FilePath
{
    NSFileManager* fileManager=[NSFileManager defaultManager];
    if([fileManager removeItemAtPath:mp3FilePath error:nil]) {
        NSLog(@"刪除");
    }
    
    @try {
        int read, write;
        
        FILE *pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb");  //source 被轉換的音頻文件位置

        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 輸出生成的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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