c++ - 如何在 iOS 中添加带有 PCM 数据/缓冲区的可播放(例如 wav、wmv) header ？

Question

我正在尝试在原始 PCM 数据之上添加一个 wav header ，以使其可以通过 AVAudioPlayer 播放。但是我找不到任何解决方案或源代码来使用 Objective-C/Swift 在 iOS 上执行此操作。虽然我找到了this但它没有正确答案。

但是我找到了一段代码here它在 C 中，也包含一些问题。从该代码生成的 wav 文件无法正常播放。

我已经在下面给出了我到目前为止编写的代码。

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，只播放前 10 到 20(大约)秒。我认为，wav header 未正确生成(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？任何帮助将不胜感激。

提前致谢。

Answer 1

好的，我正在回答我自己的问题是否对其他人有帮助。经过几天不懈的尝试，我终于让它工作了。下面是用 Objective-C 和 C 编写的完整函数。它将文件路径作为参数，其中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，后跟适当的 wav header 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