You can use external linear timecode sources for synchronization of your videos. As a hardware setup, you should send to a sound card an LTC signal.
Then, you should enable LTC timecode for your MLive or MFLive object with
(m_objMLive as IMProps).PropsSet("object::ltc.enabled", "true"); // MPlatform SDK
(myLiveSource as IMProps).PropsSet("ltc.enabled", "true"); // MFormats SDK
Once enabled, a default sound device is used as a source of the LTC signal. To change the device you should specify "ltc.audio_device" property:
(m_objMLive as IMProps).PropsSet("object::ltc.audio_device", audioDeviceName); // MPlatform SDK
(myLiveSource as IMProps).PropsSet("ltc.audio_device", audioDeviceName); // MFormats SDK
To get a list of available audio devices that can be used as LTC source, you should enumerate external audio devices.