Nothing based on time is as simple as this article implies. When movies are ripped, they tend to have slight adjustments in playback speed as a side effect, and

Nothing based on time is as simple as this article implies. When movies are ripped, they tend to have slight adjustments in playback speed as a side effect, and not necessarily at a constant rate; it can result in a total language change of a couple seconds. Any playback type analysis needs to be based on frames.