Setting Device Information in MCI

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Interested in MCI multimedia processing? First check this article out if you didn’t:

Creating a Sound Recorder in C and C#

After we received your feedbacks and comments about th.e article, we decided to add a small appendix to the end of the article about setting information (volume, channel, sampling rate, etc.) to a MCI device (a Waveform device of course.)

Like anything else in MCI, you can set device information using a MCI command (string/numeric), and this time it’s the MCI_SET command.

This command is used to set information about a specific device. This command requires an input parameter of the MCI_SET_PARMS structure. However, that input parameter might have extended members for specific devices. Because we are concentrating of Waveform devices, so we are going to use the MCI_WAVE_SET_PARMS structure that contains the extended members for our device and is defined as following:

typedef struct {
    DWORD_PTR dwCallback;
    DWORD     dwTimeFormat;
    DWORD     dwAudio;
    UINT      wInput;
    UINT      wOutput;
    WORD      wFormatTag;
    WORD      wReserved2;
    WORD      nChannels;
    WORD      wReserved3;
    DWORD     nSamplesPerSec;
    DWORD     nAvgBytesPerSec;
    WORD      nBlockAlign;
    WORD      wReserved4;
    WORD      wBitsPerSample;
    WORD      wReserved5;
} MCI_WAVE_SET_PARMS;

This structure contains all and every little piece of information that can be set to a device. I expect that you read the main article and you are already familiar with members like dwCallback (other members are self-explanatory) that we have talked about many times, and you are fine too with function calls and setting up input parameters, so I won’t get into the discussion of the structure or how you are going to use that command. However, if you need more help setting up the input parameters for the structure, you should take a brief look at the MCI_WAVE_SET_PARMS Structure documentation in the MSDN.

As you know, the MCI_WAVE_SET_PARMS unmanaged structure can be marshaled in C# as following:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct MCI_WAVE_SET_PARMS
{
    public IntPtr dwCallback;
    public uint     dwTimeFormat;
    public uint     dwAudio;
    public uint      wInput;
    public uint      wOutput;
    public ushort      wFormatTag;
    public ushort      wReserved2;
    public ushort      nChannels;
    public ushort      wReserved3;
    public uint     nSamplesPerSec;
    public uint     nAvgBytesPerSec;
    public ushort      nBlockAlign;
    public ushort      wReserved4;
    public ushort      wBitsPerSample;
    public ushort      wReserved5;
}

Congratulations! You did set the device information! So how to get them back?

This can be done through the MCI_STATUS (discussed earlier) by setting up the MCI_STATUS_ITEM flag and setting the query item to the required information you need to query about (like MCI_DGV_STATUS_VOLUME to query about volume.)

More about the MCI_STATUS command can be found in the MSDN documentation.

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