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Playing audio CDs, part 6 - MCI Command playback

  • 项目

Today, we play the actual audio track on the CD using the MCI commands.

HRESULT CMCICommandCDPlayer::PlayTrack(int TrackNumber){    MCIERROR mciError;    MCI_SET_PARMS setParms = {0};    MCI_PLAY_PARMS playParms = {0};    //    // The track number from the host app is )ORIGIN 0, MCI is )ORIGIN 1, so adjust it.    //    TrackNumber += 1;     if (TrackNumber > (int)_TrackCount)    {        printf("Track out of range\n");        return E_FAIL;    }    // Set the MCI time format to track/minute/second/frame.    setParms.dwTimeFormat = MCI_FORMAT_TMSF;    mciError = mciSendCommand(_MciHandle, MCI_SET, MCI_SET_TIME_FORMAT, (DWORD_PTR)&setParms);    if (mciError != 0)    {        printf("MCI Error %x determining CD media status\n",mciError);        return HRESULT_FROM_WIN32(mciError);    }    playParms.dwFrom = MCI_MAKE_TMSF(TrackNumber, 0, 0, 0);    if (TrackNumber < _TrackCount)    {        playParms.dwTo = MCI_MAKE_TMSF(TrackNumber+1, 0, 0, 0);    }    mciError = mciSendCommand(_MciHandle, MCI_PLAY, MCI_FROM | (TrackNumber <_TrackCount ? MCI_TO : 0) | MCI_WAIT, (DWORD_PTR)&playParms);    if (mciError != 0)    {        printf("MCI Error %x playing media\n",mciError);        return HRESULT_FROM_WIN32(mciError);    }    return S_OK;}

Not much different from the previous versions, in fact it's a pretty straightforward transcription of the previous programs.  One minor change is that I'm using the MCI_WAIT flag to ask the MCI commands

That allows me to avoid the Sleep() at the end.  I could have done the same thing in the string based version by appending the " wait" command to the play command string.

I'm going to skip a couple of days on this series, it'll take a while to get the Digital Audio Extraction version of this problem ready for publication, DAE's sufficiently compilicated that it'll take several articles to fully describe what I'm doing.

Comments

  • Anonymous
    April 27, 2005
    Out of curiosity, why didn't you use the " wait" command in the string based version? Is there a performance and/or security advantage to using a Sleep()?
  • Anonymous
    April 27, 2005
    Todd,
    Official answer? I did it to show the sync/async versions. There's no real difference between the two (but you really don't want to use the sync version in a Windows app).


    Honest answer? I didn't think of it - the WMP version needed a sleep, so I put a sleep into the MCI version :)