MCI: MCI_CLOSE needed if the CD has been ejected?

Question

Hello

I have read that sending MCI_CLOSE command is important to get access again to the device later on.

If I handle the CD player opening message DBT_DEVICEREMOVECOMPLETE, check that this is the right player (in case there are several ones) and then try to send the "mciSendCommandW(deviceID, MCI_CLOSE, MCI_WAIT, (DWORD_PTR)&mgp);" (deviceID is the same than the one I used successfully for MCI_PLAY), I get a "0xC0000008: An invalid handle was specified" exception.

Does the ejection close the device on its own before sending DBT_DEVICEREMOVECOMPLETE ?

Thanks
David

Answer 1

Finally, I cheated:

As the access to the CD player using MCI is reset once I've closed my program, I've created a console application:

• that remains hidden (with "#pragma comment(linker, "/SUBSYSTEM:WINDOWS /ENTRY:mainCRTStartup")")
• that creates a dummy window to communicate with the calling app (with "hWnd=CreateWindowExA(0, class_name, "register_name", 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, NULL, NULL);")
• that accepts 4 arguments in the command line: the letter of the CD player, the number of the first track to be played, the number of the last track and the HWND of the calling program

And then I launch it via CreateProcess from my main program. As it has the parent HWND, I "SendMessage" from it and as soon as the dummy window is created, to pass its HWND to the parent so the latter can SendMessage to the child too:

• for the parent to get the current position in the playing
• for the parent to get the length of the track
• for the parent to tell its child to Kill itself if the playing has been cancelled
• for the child to tell its parent that the song is over before lilling itself.

And it works, I can open the CD tray while it's playing, insert a new one and start with a new track with the right TOC... And it is transparent as the way I create my console app makes no window and nothing in the taskbar.
Perhaps it creates a little more delay between 2 different plays as the child app needs to be launched and the CD to be re-opened, but this is a 68kB prog so nothing unacceptable.

Thanks for your help
David

Answer 2

I just realize that if an audio CD is playing when ejecting, the last sample (in the buffer I suppose) continues to play in a loop. I can then send a MCI_STOP command (with the same deviceID) with no error and the sound stops.
If I insert another audio CD, the MCI_OPEN command returns an error, so it seems that the device has not been released... but I can't as it throws an exception even if I MCI_CLOSE just after the MCI_STOP.

If I MCI_CLOSE while the CD is still in, I have no exception, it works.

Answer 3

I also met this problem (Windows 10)
A workaround is to Lock/Unlock the CD drive with IOCTL_STORAGE_MEDIA_REMOVAL (lock when a track is playing)

Answer 4

Thanks a lot for your answer, it's a shame it can't be done the right way.
And if a track is not playing, if the CD is manually removed, there is no problem with WM_CLOSE?

Answer 5

I have checked and if the CD never played or if the playing has been stopped with a MCI_STOP, there's no problem, but if the CD is removed while playing or even after a track has stopped on its own because it was over (and even if I send a MCI_STOP afterwards), then the MCI_CLOSE crashes.

So the case of the track stopping on its own remains, even if I use your method. The only solution is to MCI_STOP just before the track is over (comparing actual play time against length) ?

EDIT: in fact if the CD has ever been played, MCI_CLOSE crashes, even if it is MCI_STOP-ped before the end...