There is a flag called the fixed_frame_rate_flag used in encoders. I haven't been able to find any clear explanation of what this is, and what its significance is. The flag can either be set to 0 or 1, but I don't know what this would imply.
Any help, information would be appreciated.
Fixed frame rate is the opposite of variable frame rate. If a video is fixed frame rate, every frame has a predictable timestamp. timestamp = frame_number * frame_rate. If its variable, every frame has its own duration and some frames may displayed for longer or shorter periods and has an unpredictable time stamp.