RAW video: skip frames on playback for more realtime review

[stevefal]

Maybe its a temporary condition and subject to more improvement, but currently playback of RAW video in-camera is at a slow frame rate, hence slo-mo. The suggestion is to purposefully skip frames in order to represent 1X playback, albeit at the low frame rate. Bonus would be to measure frame rate and calculate the skips dynamically in order to maintain as close to 1X as possible, accommodating organic variations in frame size, read rate, cpu, etc.