如何在iOS中添加PCM数据/缓冲区的可播放（如wav，wmv）标头？

时间：2015-01-30 07:28:07

标签： c++ ios objective-c c audio

我正在尝试在原始PCM数据之上添加一个wav标头，以便通过AVAudioPlayer播放它。但我无法使用Objective-C / Swift在iOS上找到任何解决方案或源代码。虽然我找到了this，但它没有正确答案。

但是我发现了一段代码here，它在C中并且还包含一些问题。 wav文件无法正常播放，该文件是从该代码生成的。

到目前为止，我已经给出了我编码的代码。

int NumChannels = AUDIO_CHANNELS_PER_FRAME;
short BitsPerSample = AUDIO_BITS_PER_CHANNEL;
int SamplingRate = AUDIO_SAMPLE_RATE;
int numOfSamples = [[NSData dataWithContentsOfFile:filePath] length];

int ByteRate = NumChannels*BitsPerSample*SamplingRate/8;
short BlockAlign = NumChannels*BitsPerSample/8;
int DataSize = NumChannels*numOfSamples*BitsPerSample/8;
int chunkSize = 16;
int totalSize = 36 + DataSize;
short audioFormat = 1;

if((fout = fopen([wavFilePath cStringUsingEncoding:1], "w")) == NULL)
{
    printf("Error opening out file ");
}

fwrite("RIFF", sizeof(char), 4,fout);
fwrite(&totalSize, sizeof(int), 1, fout);
fwrite("WAVE", sizeof(char), 4, fout);
fwrite("fmt ", sizeof(char), 3, fout);
fwrite(&chunkSize, sizeof(int),1,fout);
fwrite(&audioFormat, sizeof(short), 1, fout);
fwrite(&NumChannels, sizeof(short),1,fout);
fwrite(&SamplingRate, sizeof(int), 1, fout);
fwrite(&ByteRate, sizeof(int), 1, fout);
fwrite(&BlockAlign, sizeof(short), 1, fout);
fwrite(&BitsPerSample, sizeof(short), 1, fout);
fwrite("data", sizeof(char), 3, fout);
fwrite(&DataSize, sizeof(int), 1, fout);

文件播放速度太快，声音失真，只有前10到20秒左右正在播放。我认为，wav标头没有正确生成（因为我能够使用AudioUnit / AudioQueue播放相同的PCM数据/缓冲区）。那么我的代码中缺少什么？任何帮助都将受到高度赞赏。

提前致谢。

3 个答案:

答案 0 :(得分：10)

好的，我正在回答我自己的问题，如果它可以帮助其他人。经过几天不知疲倦的尝试，终于让它运转起来了。下面是一个用Objective-C和C编写的完整函数。它将文件路径作为参数，包含直接从麦克风捕获的RAW PCM数据，并返回包含PCM数据的文件路径，后跟相应的wav头信息。然后，您可以使用AVAudioPlayer或AVPlayer播放该文件。这是代码...... 

- (NSURL *) getAndCreatePlayableFileFromPcmData:(NSString *)filePath
{
    NSString *wavFileName = [[filePath lastPathComponent] stringByDeletingPathExtension];
    NSString *wavFileFullName = [NSString stringWithFormat:@"%@.wav",wavFileName];

    [self createFileWithName:wavFileFullName];
    NSArray *dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docsDir = [dirPaths objectAtIndex:0];
    NSString *wavFilePath = [docsDir stringByAppendingPathComponent:wavFileFullName];

    NSLog(@"PCM file path : %@",filePath);

    FILE *fout;

    short NumChannels = AUDIO_CHANNELS_PER_FRAME;
    short BitsPerSample = AUDIO_BITS_PER_CHANNEL;
    int SamplingRate = AUDIO_SAMPLE_RATE;
    int numOfSamples = [[NSData dataWithContentsOfFile:filePath] length];

    int ByteRate = NumChannels*BitsPerSample*SamplingRate/8;
    short BlockAlign = NumChannels*BitsPerSample/8;
    int DataSize = NumChannels*numOfSamples*BitsPerSample/8;
    int chunkSize = 16;
    int totalSize = 46 + DataSize;
    short audioFormat = 1;

    if((fout = fopen([wavFilePath cStringUsingEncoding:1], "w")) == NULL)
    {
        printf("Error opening out file ");
    }

    fwrite("RIFF", sizeof(char), 4,fout);
    fwrite(&totalSize, sizeof(int), 1, fout);
    fwrite("WAVE", sizeof(char), 4, fout);
    fwrite("fmt ", sizeof(char), 4, fout);
    fwrite(&chunkSize, sizeof(int),1,fout);
    fwrite(&audioFormat, sizeof(short), 1, fout);
    fwrite(&NumChannels, sizeof(short),1,fout);
    fwrite(&SamplingRate, sizeof(int), 1, fout);
    fwrite(&ByteRate, sizeof(int), 1, fout);
    fwrite(&BlockAlign, sizeof(short), 1, fout);
    fwrite(&BitsPerSample, sizeof(short), 1, fout);
    fwrite("data", sizeof(char), 4, fout);
    fwrite(&DataSize, sizeof(int), 1, fout);

    fclose(fout);

    NSMutableData *pamdata = [NSMutableData dataWithContentsOfFile:filePath];
    NSFileHandle *handle;
    handle = [NSFileHandle fileHandleForUpdatingAtPath:wavFilePath];
    [handle seekToEndOfFile];
    [handle writeData:pamdata];
    [handle closeFile];

    return [NSURL URLWithString:wavFilePath];
}

但该功能仅适用于以下音频设置。

// Audio settings.
#define AUDIO_SAMPLE_RATE 8000
#define AUDIO_FRAMES_PER_PACKET 1
#define AUDIO_CHANNELS_PER_FRAME 1
#define AUDIO_BITS_PER_CHANNEL 16
#define AUDIO_BYTES_PER_PACKET 2
#define AUDIO_BYTES_PER_FRAME 2

答案 1 :(得分：2)

非常有帮助的问题和答案，非常感谢。

此快速版本适用于需要帮助的人

static func createWAV(from pcmFilePath: String, to wavFilePath: String) -> Bool {

    // Make sure that the path does not contain non-ascii characters
    guard let fout = fopen(wavFilePath.cString(using: .ascii), "w") else { return false }

    guard let pcmData = try? Data(contentsOf: URL(fileURLWithPath: pcmFilePath)) else { return false }

    var numChannels: CShort = 1
    let numChannelsInt: CInt = 1
    var bitsPerSample: CShort = 16
    let bitsPerSampleInt: CInt = 16
    var samplingRate: CInt = 16000
    let numOfSamples = CInt(pcmData.count)
    var byteRate = numChannelsInt * bitsPerSampleInt * samplingRate / 8
    var blockAlign = numChannelsInt * bitsPerSampleInt / 8
    var dataSize = numChannelsInt * numOfSamples * bitsPerSampleInt / 8
    var chunkSize: CInt = 16
    var totalSize = 46 + dataSize
    var audioFormat: CShort = 1

    fwrite("RIFF".cString(using: .ascii), MemoryLayout<CChar>.size, 4, fout)
    fwrite(&totalSize, MemoryLayout<CInt>.size, 1, fout)
    fwrite("WAVE".cString(using: .ascii), MemoryLayout<CChar>.size, 4, fout);
    fwrite("fmt ".cString(using: .ascii), MemoryLayout<CChar>.size, 4, fout);
    fwrite(&chunkSize, MemoryLayout<CInt>.size,1,fout);
    fwrite(&audioFormat, MemoryLayout<CShort>.size, 1, fout);
    fwrite(&numChannels, MemoryLayout<CShort>.size,1,fout);
    fwrite(&samplingRate, MemoryLayout<CInt>.size, 1, fout);
    fwrite(&byteRate, MemoryLayout<CInt>.size, 1, fout);
    fwrite(&blockAlign, MemoryLayout<CShort>.size, 1, fout);
    fwrite(&bitsPerSample, MemoryLayout<CShort>.size, 1, fout);
    fwrite("data".cString(using: .ascii), MemoryLayout<CChar>.size, 4, fout);
    fwrite(&dataSize, MemoryLayout<CInt>.size, 1, fout);
    fclose(fout);

    guard let handle = FileHandle(forUpdatingAtPath: wavFilePath) else { return false }

    handle.seekToEndOfFile()
    handle.write(pcmData)
    handle.closeFile()

    return true
}

答案 2 :(得分：0)

从 qiz 对 swift 5 的回答修改

func extractSubchunks(data:Data) -> RiffFile? {
    var data = data
    var chunks = [SubChunk]()
    let position = data.subdata(in: 8..<12)
    let filelengthBytes = data.subdata(in: 4..<8).map { UInt32($0) }
    let filelength: UInt32 = filelengthBytes[0] << 24 + filelengthBytes[1] << 16 + filelengthBytes[2] << 8 + filelengthBytes[3]
    let wave = String(bytes: position, encoding: .utf8) ?? "NoName"
    guard wave == "WAVE" else {
        print("File is \(wave) not WAVE")
        return nil
    }
    data.removeSubrange(0..<12)
    print("Found chunks")
    while data.count != 0{
        let position = data.subdata(in: 0..<4)
        let lengthBytes = data.subdata(in: 4..<8).map { UInt32($0) }
        let length: UInt32 = lengthBytes[0] << 24 + lengthBytes[1] << 16 + lengthBytes[2] << 8 + lengthBytes[3]
        guard let current = String(bytes: position, encoding: .utf8) else{
            return nil
        }
        data.removeSubrange(0..<8)
        let chunkData = data.subdata(in: 0..<Int(length))
        data.removeSubrange(0..<Int(length))
        let subchunk = SubChunk(name: current, size: Int(length), data: chunkData)
        chunks.append(subchunk)
        print(subchunk.debugDescription)
    }
    let riff = RiffFile(size: Int(filelength), subChunks: chunks)
    return riff
}
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