I applied for CSA On-Board October 2013, and last year I did a Video interview. All I will say is make sure your wearing a shirt and tie, as you would at a normal interview. Just be yourself. The questions are in text form, and you are given a time frame to talk into your microphone on your computer. I completed this a year ago, and was soon invited to York for an interview and assessment. Unfortunately for my disappointment, I did not get the job, and neither did I get past the application stage for trainee conductor either.
On that not good luck, as it is not daunting as it sounds.