Question

这是来自Learning Core Audio http://www.amazon.com/Learning-Core-Audio-Hands-On-Programming/dp/0321636848的代码就像书中所说，生成立体声应该将asbd.mBitsPerChannel设置为8，将asbd.mChannelsPerFrame设置为2。但我得到的音频只有一个频道。我不知道代码有什么问题，请帮帮我。感谢

#import <Foundation/Foundation.h>
#import <AudioToolbox/AudioToolbox.h>

#define SAMPLE_RATE 44100
#define DURATION 5.0
#define FILENAME_FORMAT @"%0.3f-square.aif"

int main(int argc, const char * argv[])
{

@autoreleasepool {
    if (argc < 2) {
        printf("Usage: CAToneFileGenerator n\n(where n is tone in Hz)");
        return -1;
    }

    double hz = atof(argv[1]);
    assert(hz > 0);
    NSLog(@"generating %f hz tone", hz);

    NSString *fileName = [NSString stringWithFormat:FILENAME_FORMAT, hz];
    NSString *filePath = [[[NSFileManager defaultManager] currentDirectoryPath] stringByAppendingPathComponent:fileName];
    NSLog(@"%@", filePath);
    NSURL *fileURL = [NSURL fileURLWithPath:filePath];

    AudioStreamBasicDescription asbd;
    memset(&asbd, 0, sizeof(asbd));
    asbd.mSampleRate = SAMPLE_RATE;
    asbd.mFormatID = kAudioFormatLinearPCM;
    asbd.mFormatFlags = kAudioFormatFlagIsBigEndian | kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    asbd.mBitsPerChannel = 8;
    asbd.mChannelsPerFrame = 2;
    asbd.mFramesPerPacket = 1;
    asbd.mBytesPerFrame = 2;
    asbd.mBytesPerPacket = 2;

    AudioFileID audioFile;
    OSStatus audioErr = noErr;
    audioErr = AudioFileCreateWithURL((CFURLRef) fileURL, kAudioFileAIFFType, &asbd, kAudioFileFlags_EraseFile, &audioFile);
    assert(audioErr == noErr);

    long maxSampleCount = SAMPLE_RATE * DURATION;
    long sampleCount = 0;
    UInt32 bytesToWrite = 2;
    double wavelengthInSamples = SAMPLE_RATE / hz;

    while (sampleCount < maxSampleCount) {
        for (int i = 0; i < wavelengthInSamples; i++) {
            SInt16 sample;
            if (i < wavelengthInSamples /2) {
                sample = CFSwapInt16HostToBig(SHRT_MAX);
            }else{
                sample = CFSwapInt16HostToBig(SHRT_MIN);
            }

            audioErr = AudioFileWriteBytes(audioFile, false, sampleCount*2, &bytesToWrite, &sample);
            assert(audioErr == noErr);
            sampleCount ++;
        }
    }
    audioErr = AudioFileClose(audioFile);
    assert(audioErr == noErr);
    NSLog(@"wrote %ld samples", sampleCount);
}
return 0;
}

Answer 1

只是从书籍代码更改ASBD并不会神奇地修复所有内容。您还没有考虑如何将样本写入文件。此外，8位听起来像屁股。

回到mBitsPerChannel = 16，然后说明你每帧写两个频道的事实，这意味着mBytesPerFrame和mBytesPerPacket现在将是4（书中它们是2）。想想为什么会这样。

然后你应该只能添加对AudioFileWriteBytes（）的第二次调用 - 或者在你计算mChannelsPerFrame的循环之后 - 在第一次调用之后。但是你必须考虑文件中的不同偏移，因为你每次写入4个字节而不是2个。我认为这是正确的：

  audioErr = AudioFileWriteBytes(audioFile, false, sampleCount*4, &bytesToWrite, &sample); // left
  audioErr = AudioFileWriteBytes(audioFile, false, (sampleCount*4)+2, &bytesToWrite, &sample); // right

你需要自己弄清楚这些东西才能让它沉入其中。

核心音频如何用双声道（立体声）生成方波

1 个答案: