iOS: Audio File 音频文件录制(支持VBR,CBR)

需求：iOS中使用Audio File 实现音频文件录制.

---

实现原理: 使用Audio File中的API可以将我们采集到的音频数据录制成音频文件,这里采集到的数据包括从Audio Queue/Audio Unit直接采集或Audio Converter间接转换得到的音频数据.

---

阅读前提:

• 本文需要借助三种数据源以实现音频数据录制: Audio Queue, Audio Converter
• Core Audio基本原理:,掘金,博客
• 音频采集: Audio Queue ,掘金,博客
• 音频采集: Audio Unit ,掘金,博客
• C,C++基本知识

本文直接为实战篇,如需了解理论基础参考上述链接中的内容,本文侧重于实战中注意点.

本项目需要借助Audio Queue, Audio Unit的采集,才能实现录制.所以提供以下两个Demo.

---

GitHub地址(附代码) : Audio Queue录制, Audio Unit录制

地址 : Audio File Record

掘金地址 : Audio File Record

博客地址 : Audio File Record

---

具体实现

1. 创建音频文件

这里使用当前格式化时间作为文件名,命名冲突.

下面主要代码为创建一个用于存放声音的音频文件,主要是在沙盒中创建一个目录(名为Voice)存放音频文件.注意,我们一定要先将文件夹创建出来,否则在调用后面AudioFileCreateWithURL函数时将报错.

- (NSString *)createFilePath {
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"yyyy_MM_dd__HH_mm_ss";
    NSString *date = [dateFormatter stringFromDate:[NSDate date]];
    
    NSArray *searchPaths    = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                                  NSUserDomainMask,
                                                                  YES);
    
    NSString *documentPath  = [[searchPaths objectAtIndex:0] stringByAppendingPathComponent:@"Voice"];
    
    // 先创建子目录. 注意,若果直接调用AudioFileCreateWithURL创建一个不存在的目录创建文件会失败
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if (![fileManager fileExistsAtPath:documentPath]) {
        [fileManager createDirectoryAtPath:documentPath withIntermediateDirectories:YES attributes:nil error:nil];
    }
    
    NSString *fullFileName  = [NSString stringWithFormat:@"%@.caf",date];
    NSString *filePath      = [documentPath stringByAppendingPathComponent:fullFileName];
    return filePath;
}

2. 创建Audio File

通过上面创建的url,再加上我们要创建的文件类型(iOS中CAF格式文件可以存放任意类型音频数据),音频流的ASBD格式,文件特性的flag,这里设置kAudioFileFlags_EraseFile表明CreateURL调用将清空现有文件的内容,如果未设置，则如果文件已存在则CreateURL调用将失败.

- (AudioFileID)createAudioFileWithFilePath:(NSString *)filePath AudioDesc:(AudioStreamBasicDescription)audioDesc {
    CFURLRef url            = CFURLCreateWithString(kCFAllocatorDefault, (CFStringRef)filePath, NULL);
    NSLog(@"Audio Recorder: record file path:%@",filePath);
    
    AudioFileID audioFile;
    // create the audio file
    OSStatus status = AudioFileCreateWithURL(url,
                                             kAudioFileCAFType,
                                             &audioDesc,
                                             kAudioFileFlags_EraseFile,
                                             &audioFile);
    if (status != noErr) {
        NSLog(@"Audio Recorder: AudioFileCreateWithURL Failed, status:%d",(int)status);
    }
    
    CFRelease(url);
    
    return audioFile;
}

3. 设置magic cookie

magic cookie: 可以理解成是文件的头信息,包含音频文件播放需要的一些必要信息, magic cookie块包含某些音频数据格式（例如MPEG-4 AAC）所需的补充数据，用于解码音频数据。如果CAF文件中包含的音频数据格式需要magic cookie数据，则该文件必须具有此块。

在这里分为两种情况,如果录制文件数据CBR(未压缩数据格式:PCM...),则不需要设置magic cookie, 如果录制文件数据VBR(压缩数据格式:AAC...),则需要设置magic cookie.

注意: 采用不同技术采集到的音频,设置magic cookie的方式是不同的.

• Audio Queue 设置magic cookie

首先使用kAudioQueueProperty_MagicCookie属性获取当前audio queue是否含有magic cookie,如果有,返回magic cookie长度,然后为它分配一段内存就可以调用kAudioQueueProperty_MagicCookie获取audio queue中的magic cookie,最后,将magic cookie通过kAudioFilePropertyMagicCookieData属性设置到audio file中即可.

- (void)copyEncoderCookieToFileByAudioQueue:(AudioQueueRef)inQueue inFile:(AudioFileID)inFile {
    OSStatus result = noErr;
    UInt32 cookieSize;
    
    result = AudioQueueGetPropertySize (
                                        inQueue,
                                        kAudioQueueProperty_MagicCookie,
                                        &cookieSize
                                        );
    if (result == noErr) {
        char* magicCookie = (char *) malloc (cookieSize);
        result =AudioQueueGetProperty (
                                       inQueue,
                                       kAudioQueueProperty_MagicCookie,
                                       magicCookie,
                                       &cookieSize
                                       );
        if (result == noErr) {
            result = AudioFileSetProperty (
                                           inFile,
                                           kAudioFilePropertyMagicCookieData,
                                           cookieSize,
                                           magicCookie
                                           );
            if (result == noErr) {
                NSLog(@"set Magic cookie successful.");
            }else {
                NSLog(@"set Magic cookie failed.");
            }
        }else {
            NSLog(@"get Magic cookie failed.");
        }
        free (magicCookie);
            
    }else {
        NSLog(@"Magic cookie: get size failed.");
    }

}

• Audio Converter 设置magic cookie

当使用Audio Unit采集音频数据时,我们无法直接采集AAC类型的数据,需要借助Audio Converter,原理同上,即从Audio Converter中获取Magic cookie并设置给audio file.

-(void)copyEncoderCookieToFileByAudioConverter:(AudioConverterRef)audioConverter inFile:(AudioFileID)inFile {
    // Grab the cookie from the converter and write it to the destination file.
    UInt32 cookieSize = 0;
    OSStatus error = AudioConverterGetPropertyInfo(audioConverter, kAudioConverterCompressionMagicCookie, &cookieSize, NULL);
    
    if (error == noErr && cookieSize != 0) {
        char *cookie = (char *)malloc(cookieSize * sizeof(char));
        error        = AudioConverterGetProperty(audioConverter, kAudioConverterCompressionMagicCookie, &cookieSize, cookie);
        
        if (error == noErr) {
            error = AudioFileSetProperty(inFile, kAudioFilePropertyMagicCookieData, cookieSize, cookie);
            if (error == noErr) {
                UInt32 willEatTheCookie = false;
                error = AudioFileGetPropertyInfo(inFile, kAudioFilePropertyMagicCookieData, NULL, &willEatTheCookie);
                if (error == noErr) {
                    NSLog(@"%@:%s - Writing magic cookie to destination file: %u   cookie:%d \n",kModuleName,__func__, (unsigned int)cookieSize, willEatTheCookie);
                }else {
                    NSLog(@"%@:%s - Could not Writing magic cookie to destination file status:%d \n",kModuleName,__func__,(int)error);
                }
            } else {
                NSLog(@"%@:%s - Even though some formats have cookies, some files don't take them and that's OK,set cookie status:%d \n",kModuleName,__func__,(int)error);
            }
        } else {
            NSLog(@"%@:%s - Could not Get kAudioConverterCompressionMagicCookie from Audio Converter!\n status:%d ",kModuleName,__func__,(int)error);
        }
        
        free(cookie);
    }else {
        // If there is an error here, then the format doesn't have a cookie - this is perfectly fine as som formats do not.
        NSLog(@"%@:%s - cookie status:%d, %d \n",kModuleName,__func__,(int)error, cookieSize);
    }
}

4. 将数据写入文件.

通过AudioFileWritePackets可以将音频数据写入文件.

- (void)writeFileWithInNumBytes:(UInt32)inNumBytes ioNumPackets:(UInt32 )ioNumPackets inBuffer:(const void *)inBuffer inPacketDesc:(const AudioStreamPacketDescription*)inPacketDesc {
    if (!m_recordFile) {
        return;
    }
    
//    AudioStreamPacketDescription outputPacketDescriptions;
    OSStatus status = AudioFileWritePackets(m_recordFile,
                                            false,
                                            inNumBytes,
                                            inPacketDesc,
                                            m_recordCurrentPacket,
                                            &ioNumPackets,
                                            inBuffer);
    
    if (status == noErr) {
        m_recordCurrentPacket += ioNumPackets;  // 用于记录起始位置
    }else {
        NSLog(@"%@:%s - write file status = %d \n",kModuleName,__func__,(int)status);
    }
    
}

该函数定义如下.

• inUseCache: 写入数据时是否缓存数据
• inNumBytes: 写入数据的大小
• inPacketDescriptions: VBR格式下音频数据包的描述信息
• inStartingPacket: 每次从第多少个包开始写入,累加过程,所以需要记录
• ioNumPackets:当前这次写入多少个数据包
• inBuffer: 写入的音频数据

extern OSStatus 
AudioFileWritePackets ( AudioFileID                         inAudioFile,  
                        Boolean                             inUseCache,
                        UInt32                              inNumBytes,
                        const AudioStreamPacketDescription * __nullable inPacketDescriptions,
                        SInt64                              inStartingPacket, 
                        UInt32                              *ioNumPackets, 
                        const void                          *inBuffer)          API_AVAILABLE(macos(10.2), ios(2.0), watchos(2.0), tvos(9.0));

5. 停止录制

注意: 在开启与关闭录制时都需要做一次写magic cookie操作,开始时做是为了使文件具备magic cookie可用,结束时调用是为了更新与校正magic cookie信息.

-(void)stopVoiceRecordAudioConverter:(AudioConverterRef)audioConverter needMagicCookie:(BOOL)isNeedMagicCookie {
    if (isNeedMagicCookie) {
        // reconfirm magic cookie at the end.
        [self copyEncoderCookieToFileByAudioConverter:audioConverter
                                               inFile:m_recordFile];
    }
    
    AudioFileClose(m_recordFile);
    m_recordCurrentPacket = 0;
}