John Asks: So why does VBR cause so many problems with regard to the accuracy of playback when creating depo clips?
One issue with variable bit rate is the ability to determine the location by the application. Typically when a video is loaded into a player the file is sampled for only the first part and then the entire length is determined by dividing the sample size into the total bit count for the file. An easy math example is say the first second is 10 kb and the file is 1,000 kb then the software estimates the total length at 100 seconds and 90 seconds into the file is located at bit number 900. With variable bit rate this calculation is not necessarily accurate.
So why does this matter when creating deposition video synched to the transcript? When you seek to a spot in the file the calculation is used for the jump. So if the calculation is inaccurate there is a delay introduced for the extra time needed by the player to find the designated location. You make a clip and the synch information says it is 58 minutes into the file. The player jumps to the calculated, by bit rate, time location but that is not correct so it must adjust the start until it finds the proper location to start playing the clip. It plays fine but you have introduced the possibility of a delay to find the start. Clients don‘t like delays, the court does not appreciate them either.