C# Definition:

/// <summary>
    /// The MIXERLINE structure describes the state and metrics of an audio line.
    /// </summary>
    public struct MIXERLINE
    {
    /// <summary>
    /// Size, in bytes, of the MIXERLINE structure. This member must be
    /// initialized before calling the mixerGetLineInfo function.
    /// The size specified in this member must be large enough to contain the
    /// MIXERLINE structure. When mixerGetLineInfo returns,
    /// this member contains the actual size of the information returned.
    /// The returned information will not exceed the requested size.
    /// </summary>
    public uint cbStruct;
    /// <summary>
    /// Destination line index. This member ranges from zero to one less than
    /// the value specified in the cDestinations member of the MIXERCAPS structure
    /// retrieved by the mixerGetDevCaps function. When the mixerGetLineInfo function
    /// is called with the MIXER_GETLINEINFOF_DESTINATION flag, properties for the
    /// destination line are returned. (The dwSource member must be set to zero in
    /// this case.) When called with the MIXER_GETLINEINFOF_SOURCE flag,
    /// the properties for the source given by the dwSource member that is
    /// associated with the dwDestination member are returned.
    /// </summary>
    public uint dwDestination;
    /// <summary>
    /// Index for the audio source line associated with the dwDestination member.
    /// That is, this member specifies the nth audio source line associated with
    /// the specified audio destination line. This member is not used for destination
    /// lines and must be set to zero when MIXER_GETLINEINFOF_DESTINATION is
    /// specified in the mixerGetLineInfo function. When the MIXER_GETLINEINFOF_SOURCE
    /// flag is specified, this member ranges from zero to one less than the value
    /// specified in the cConnections member for the audio destination line given in
    /// the dwDestination member.
    /// </summary>
    public uint dwSource;
    /// <summary>
    /// An identifier defined by the mixer device that uniquely refers to the audio
    /// line described by the MIXERLINE structure. This identifier is unique for each
    /// mixer device and can be in any format. An application should use this identifier
    /// only as an abstract handle.
    /// </summary>
    public uint dwLineID;
    /// <summary>
    /// Status and support flags for the audio line. This member is always returned
    /// to the application and requires no initialization.
    ///
    /// <para>
    /// MixerLineFlags value
    /// </para>
    /// <para>
    /// If an application is not using a waveform-audio output device, the audio line
    /// associated with that device would not be active
    /// (that is, the MIXERLINE_LINEF_ACTIVE flag would not be set).
    /// If the waveform-audio output device is opened, then the audio line
    /// is considered active and the MIXERLINE_LINEF_ACTIVE flag will be set.
    /// A paused or starved waveform-audio output device is still considered active.
    /// In other words, if the waveform-audio output device is opened by an application
    /// regardless of whether data is being played, the associated audio line is
    /// considered active.
    /// If a line cannot be strictly defined as active, the mixer device will always
    /// set the MIXERLINE_LINEF_ACTIVE flag.
    /// </para>
    /// </summary>
    public uint fdwLine;
    /// <summary>
    /// Instance data defined by the audio device for the line.
    /// This member is intended for custom mixer applications designed specifically
    /// for the mixer device returning this information. Other applications should
    /// ignore this data.
    /// </summary>
    public uint dwUser;
    /// <summary>
    /// Component type for this audio line. An application can use this information
    /// to display tailored graphics or to search for a particular component.
    /// If an application does not use component types, this member should be
    /// ignored. This member can be one of the following values:
    ///
    /// <para>MIXERLINE_COMPONENT_TYPE value</para>
    /// </summary>
    public uint dwComponentType;
    /// <summary>
    /// Maximum number of separate channels that can be manipulated independently
    /// for the audio line. The minimum value for this field is 1 because a
    /// line must have at least one channel.
    /// <para>
    /// Most modern audio cards for personal computers are stereo devices; for
    /// them, the value of this member is 2.
    /// </para>
    /// <para>
    /// Channel 1 is assumed to be the left channel; channel 2 is assumed to be
    /// the right channel.
    /// </para>
    /// <para>
    /// A multichannel line might have one or more uniform controls
    /// (controls that affect all channels of a line uniformly) associated with it.
    /// </para>
    /// </summary>
    public uint cChannels;
    /// <summary>
    /// Number of connections that are associated with the audio line. This member
    /// is used only for audio destination lines and specifies the number of audio
    /// source lines that are associated with it. This member is always zero for
    /// source lines and for destination lines that do not have any audio source
    /// lines associated with them.
    /// </summary>
    public uint cConnections;
    /// <summary>
    /// Number of controls associated with the audio line. This value can be zero.
    /// If no controls are associated with the line, the line is likely to be a
    /// source that might be selected in a MIXERCONTROL_CONTROLTYPE_MUX or
    /// MIXERCONTROL_CONTROLTYPE_MIXER but allows no manipulation of the signal.
    /// </summary>
    public uint cControls;
    /// <summary>
    /// Short string that describes the audio mixer line specified in the
    /// dwLineID member. This description should be appropriate as a concise
    /// label for the line.
    /// </summary>
    public char[] szShortName;
    /// <summary>
    /// String that describes the audio mixer line specified in the dwLineID member.
    /// This description should be appropriate as a complete description for the line.
    /// </summary>
    public char[] szName;

    /// <summary>
    /// Target media information.
    /// </summary>
    public struct Target
    {
        /// <summary>
        /// Target media device type associated with the audio line described in the
        /// MIXERLINE structure.
        /// An application must ignore target information for media
        /// device types it does not use.
        /// <para>
        /// The following values are defined: MIXERLINE_DEVICE value
        /// </para>
        /// </summary>
        public uint dwType;
        /// <summary>
        /// Current device identifier of the target media device when the dwType member
        /// is a target type other than MIXERLINE_TARGETTYPE_UNDEFINED. This identifier
        /// is identical to the current media device index of the associated media
        /// device. When calling the mixerGetLineInfo function with the
        /// MIXER_GETLINEINFOF_TARGETTYPE flag, this member is ignored on input
        /// and will be returned to the caller by the audio mixer manager.
        /// </summary>
        public uint dwDeviceID;
        /// <summary>
        /// Manufacturer identifier of the target media device when the dwType member
        /// is a target type other than MIXERLINE_TARGETTYPE_UNDEFINED.
        /// This identifier is identical to the wMid member of the device-capabilities
        /// structure for the associated media. Manufacturer identifiers are defined
        /// in Manufacturer and Product Identifiers.
        /// </summary>
        public uint wMid;
        /// <summary>
        /// Product identifier of the target media device when the dwType member
        /// is a target type other than MIXERLINE_TARGETTYPE_UNDEFINED.
        /// This identifier is identical to the wPid member of the device-capabilities
        /// structure for the associated media. Product identifiers are defined in Manufacturer and Product Identifiers.
        /// </summary>
        public uint wPid;
        /// <summary>
        /// Driver version of the target media device when the dwType member is a
        /// target type other than MIXERLINE_TARGETTYPE_UNDEFINED. This version is
        /// identical to the vDriverVersion member of the device-capabilities structure
        /// for the associated media.
        /// </summary>
        public string vDriverVersion;
        /// <summary>
        /// Product name of the target media device when the dwType member is a
        /// target type other than MIXERLINE_TARGETTYPE_UNDEFINED. This name is
        /// identical to the szPname member of the device-capabilities structure
        /// for the associated media.
        /// </summary>
        public char[] szPname;
    }
    }