请教:DSound中建立缓冲区总是出现DSERR_BADFORMAT,请教原因

s_51563946

    在Dsound中建立缓冲区(CreateSoundBuffer)总是提示我格式错误.我填写的格式方法如下:
    音频的结构为
    WAVEFORMATEX wfx;
    memset(&wfx, 0, sizeof(WAVEFORMATEX));
    wfx.wFormatTag = WAVE_FORMAT_PCM;
    wfx.nChannels = decoder->channels();
    wfx.wBitsPerSample = decoder->sample_bit();
    wfx.nSamplesPerSec = decoder->frequency();
    wfx.nBlockAlign = wfx.nChannels*wfx.wBitsPerSample/8;
    wfx.nAvgBytesPerSec = wfx.nSamplesPerSec * wfx.nBlockAlign;

这些在运行期的数值是:
    wfx.wFormatTag = 1
    wfx.nChannels = 2
    wfx.wBitsPerSample = 16
    wfx.nSamplesPerSec = 44100
    wfx.nBlockAlign = 4
    wfx.nAvgBytesPerSec = 176400

缓冲区的属性为:
    DSBUFFERDESC dsbdesc;
    memset(&dsbdesc, 0, sizeof(DSBUFFERDESC));
        dsbdesc.dwSize = sizeof(dsbdesc);
    dsbdesc.dwFlags = DSBCAPS_GLOBALFOCUS | DSBCAPS_CTRLPOSITIONNOTIFY |
        DSBCAPS_GETCURRENTPOSITION2 | DSBCAPS_CTRL3D;
    dsbdesc.dwBufferBytes = block_size*block_num;
    dsbdesc.lpwfxFormat = &wfx;
    其中block_size = 4096*8, block_num = 2.
不知道这样填写有什么问题,老是出错.而另一个单声道的音频文件打开又是正确的,其中数据为:
    wfx.wFormatTag = 1
    wfx.nChannels = 1
    wfx.wBitsPerSample = 16
    wfx.nSamplesPerSec = 44100
    wfx.nBlockAlign = 2
    wfx.nAvgBytesPerSec = 88200
哪位达人能告诉我为什么,谢谢了!!

s_51563946

算了,我知道了.DSBCAPS_CTRL3D不支持双通道