KVM Support

The NDI advanced SDK includes support for controlling a remote KVM enabled device over NDI. This SDK allows you to send keyboard, mouse, clipboard, and touch messages to a sender that is marked as supporting these messages. This functionality is implemented on an NDI receiver and messages are sent from this to a sender to offer KVM control.

It is critical that you test any applications you have very thoroughly since full support of a remote machine is not simple and has many edge cases that are hard to ensure solve -- for instance for every keyboard and mouse "press" there must also be a corresponding "release message" or the remote machine will interpret this as a "stuck key".

The following documentation describes all the relevant functions required for KVM control.

bool NDIlib_recv_kvm_is_supported(NDIlib_recv_instance_t p_instance);

This function will tell you whether the current source that this receiver is connected to is able to be KVM controlled. The value returned by this function might change based on whether the remote source currently has KVM enabled or not. If you are receiving data from the video source using NDIlib_recv_capture_v2, then you will be notified of a potential change of KVM status when that function returns NDIlib_frame_type_status_change.

bool NDIlib_recv_kvm_send_left_mouse_click(NDIlib_recv_instance_t p_instance);
bool NDIlib_recv_kvm_send_middle_mouse_click(NDIlib_recv_instance_t p_instance);
bool NDIlib_recv_kvm_send_right_mouse_click(NDIlib_recv_instance_t p_instance);

When you want to send a mouse down (i.e., a mouse click has been started) message to the source that this receiver is connected too then you would call this function. There are individual functions to allow you to send a mouse click message for the left, middle and right mouse buttons. To simulate a double-click operation you would send three messages; the first two would be mouse click messages with the third being the mouse release message. It is important that for each click message there must be at least one mouse release message or the operating system that you are connected to will continue to believe that the mouse button remains pressed forever.

bool NDIlib_recv_kvm_send_left_mouse_release(NDIlib_recv_instance_t p_instance);
bool NDIlib_recv_kvm_send_middle_mouse_release(NDIlib_recv_instance_t p_instance);
bool NDIlib_recv_kvm_send_right_mouse_release(NDIlib_recv_instance_t p_instance);

When you wish to send a mouse release message to a source, then you will call one of these functions. They simulate the release of a mouse message and would always be sent after a mouse click message has been sent.

bool NDIlib_recv_kvm_send_vertical_mouse_wheel(
    NDIlib_recv_instance_t p_instance, const float no_units
);
bool NDIlib_recv_kvm_send_horizontal_mouse_wheel(
    NDIlib_recv_instance_t p_instance, const float no_units
);

To simulate a mouse-wheel update you will call this function. You may simulate either a vertical or a horizontal wheel update which are separate controls on most platforms. The floating-point unit represents the number of "units" that you wish the mouse-wheel to be moved, with 1.0 representing a downwards or right-hand single unit.

bool NDIlib_recv_kvm_send_mouse_position(
    NDIlib_recv_instance_t p_instance, const float posn[2]
);

To set the mouse cursor position you will call this this function. The coordinates are specified in resolution independent settings in the range 0.0 - 1.0 for the current display that you are connected to. The resolution of the screen can be known if you are receiving the video source from that device, and this might change on the fly of course. Position (0,0) is the top left of the screen. posn[0] is the x-coordinate of the mouse cursor, posn[1] is the x-coordinate of the mouse cursor.

bool NDIlib_recv_kvm_send_clipboard_contents(
    NDIlib_recv_instance_t p_instance, const char* p_clipboard_contents
);

In order to send a new "clipboard buffer" to the destination one would call this function and pass a null terminated string that represents the text to be placed on the destination machine buffer.

bool NDIlib_recv_kvm_send_touch_positions(
    NDIlib_recv_instance_t p_instance, const int no_posns, const float posns[]
);

This function will send a touch event to the source that this receiver is connected to. There can be any number of simultaneous touch points in an array that is transmitted. The value of no_posns represents how many current touch points are used, and the array of posns[] is a list of the [x,y] coordinates in floating point of the touch positions. These positions are processed at a higher precision that the screen resolution on many systems, with (0,0) being the top-left corner of the screen and (1,1) being the bottom-right corner of the screen. As an example, if there are two touch positions, then posns[0] would be the x-coordinate of the first position, posns[1] would be the y-coordinate of the first position, posns[2] would be the x-coordinate of the second position, posns[2] would be the y-coordinate of the second position.

bool NDIlib_recv_kvm_send_keyboard_press(
    NDIlib_recv_instance_t p_instance, const int key_sym_value
);

To send a keyboard press event, this function is called. Keyboard messages use the standard X-Windows Keysym values. A copy of the standard define that is used for these is included in the NDI SDK for your convenience with the filename "Processing.NDI.KVM.keysymdef.h". Since this file includes many #defines, it is not included by default when you simply include the NDI SDK files, if you wish it to be included you may #define the value NDI_KVM_INCLUDE_KEYSYM or simply include this file into your application manually. For every key press event it is important to also send a keyboard release event, or the destination will believe that there is a "stuck key"! Additional information about keysym values may easily be located online, for instance https://www.tcl.tk/man/tcl/TkCmd/keysyms.html

bool NDIlib_recv_kvm_send_keyboard_release(
    NDIlib_recv_instance_t p_instance, const int key_sym_value
);

Once you wish a keyboard value to be "release" then one simply sends the matching keyboard release message with the associated key-sym value.