How can output to external device in realtime (ieee-1394 or xinerama)?

You can not output to FireWire in real time and this is not planned as Kdenlive is not a strictly DV or HDV editor and it is too intensive to conform, encode, and output to those formats in real-time. Or, put another way - the effort to make that all work well is not worth it compared where else effort can be applied. If using multi-monitor, you can extend the desktop and undock the monitor panels. The only other "external device" I currently may add support for is an SDI card since I already have some support for them in MLT - I just need to add a multi-output capability and/or alter Kdenlive to allow output to SDI.