Frame Timing in Filter

[sprite2005]

Not really an issue but was wondering if there is any way to get current frame timestamp or time elapsed since last frame in the onDraw call in a filter, or what would be the best approach for adding this either as a fork or pull request. Specifically my use case I'm overlaying a gif on the video and need to advance frames at the proper rate, but I'm sure it could be useful for other time based effects/animations also.