For generating the video signals for this project we are going to use simple voltage dividers to provide the correct amplitude and output impedance.
To calculate such values we should start by analyzing the voltages and currents involved.

We are considering signals with a peak voltage of 0.8Volts with a 75 Ohms load because this is the amplitude of the video portion of a standard 1Vpp composite video signal (being the 0.2Volts below zero the amplitude of the sync tip). Without any load the peak amplitude of the video shall be twice that value (1.6V)
On the calculation we must also consider the output voltage of the microcontroller which is typically below Vcc.

After the calculation we came close to two standard resistor values.