Kdenlive provides functionality for capturing video from external devices - Firewire, FFmpeg, Screen Grab and Blackmagic.
You configure video capturing from here).(more on this
You define the location your captures will end up using here).(more on this
To execute a video capture select the Record Monitor and choose the capture device from the drop down in the bottom right.
This captures video from sources connected via a firewire (also known as - IEEE 1394 High Speed Serial Bus) card and cable. This functionality uses the dvgrab program and the settings for this can be customized by clicking the spanner icon or choosing See Configure Firewire Capture
To perform a capture:
Note: If your device does not start playing the source device when you click the record button then you may have to start playback on your device manually and then click record.
I believe this captures video from an installed Web Cam using Video4Linux2.
This captures video of the PC screen. In version 0.9.2 it uses recordMyDesktop to do the capture. There is an open defect with this functionality in ver 0.9.2 - See bug tracker ID 2643.
In version 0.9.3 the Screen grab is done by the ffmpeg functionality instead. For screen capture to work in ver 0.9.3 the version of ffmpeg installed needs to have been compiled with the --enable-x11grab option. Ubuntu comes with an ffmpeg compiled with this option.
To check on your linux distro type "ffmpeg -version" in a terminal and look for --enable-x11grab in the reported configuration info. 
If you are capturing screen and using the X246 with audio settings and you get a crash as shown in the screen shot ...
... then consider creating a profile for audio capture where -acodec pcm_s16le is replaced by -acodec libvorbis -b 320k. See Configure Kdnelive