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Time Lapse Formula

This question keeps getting asked so I thought I would post the information for easy reference.

When doing interval recording with my video camera (DVX100) I use the following formulas for calculating recording. There are two formulas.

-- Formula 1 --

Here's an example. If you want record 24 hours and have it reduced and displayed in 1 minute at 30fps then you have the formula:

    LPF = Length in time per frame.

    FPS = frames per second

    TL  = Total Length in time (seconds) to record


    LPF * FPS * 60 seconds = TL

or

    LPF = TL / (FPS * 60 seconds)

Given the example values above:

    LPF = 86400 seconds / (30fps * 60 secs)

    LPF = 48 seconds

So, you want to shoot a frame every 48 secs for an hour.

But, the DVX only allows capturing at 30p or 60i when doing interval mode. Too bad 24fps isn't supported, otherwise the above formula would equal a frame every 60 seconds.

I have shot several hour time lapses using the 1 minute interval and a 0.5 sec recording time. A 0.5 sec rec time is the minimum supported.

Note that when you acquire your video you will actually have multiple frames for each interval. Shooting 30p at the 0.5 sec setting you will give you 15 frames. In post you will need to speed up the clip to remove the additional frames.

-- Formula 2 --

You capture 2 hours and want to show this reduced to how long? Let's say you want it reduced to 30 seconds. Now what's the framerate of your final output? 60? That means you will need:

    (30seconds) * (60 frames/second) = 1800 frames of video

Next, calculate the interval for the total time of 2 hours but converted to seconds:

    (2 hours) * (60minutes/1hr) * (60seconds/1hr) = 7200 seconds

Finally, divide the total time by the required frames:

    (7200 seconds) / (1800 frames) = 4 seconds / frame

Therefore you will need to shoot one frame every 4 seconds. But, the DVX only supports shooting a minimum interval of 15 seconds. So what to do? Well, you could change the length of time you want the final time lapse. Or, you could record normally and switch tapes when the first is almost done. Then import both and reduce in post.

Here's one of the time lapse sunsets I have done:

Goodbye Cruel World Music Video

Cheers!