I have never done this. But the theory seems to be pretty simple. Assuming that the LCD controller chip has (x,y) and Amplitude input lines:
In a CRT display, X, Y and Video inputs are all analog. So it is evident that we will need to convert this to Digital to be used in an LCD display.
X and Y simply represent the position. So a simple high speed ADC should do the trick.
The video signal (to make it simple let us assume it is a monochromatic signal) represents the brightness of the pixel represented by the X and Y signals. So a digitally converted video signal can do the job for the pixel brightness as well.
You will need to decide the sampling speed of the ADC based on the video stream bandwidth.
Please note that the three signals should be highly synchronized (so keep the signal lines as similar as possible regarding physical dimensions).
Hope this helps.