[FFmpeg-user] “Real Time”, “Slow Motion” and “Time Lapse”

Nicolas George george at nsup.org
Tue May 11 00:26:37 EEST 2021

Bryce Newman (12021-05-10):
> I have - for example - three videos that which visually can be classified as “Real Time”, “Slow Motion” and “Time Lapse”.
> My understanding is the speed of the video is controlled by the filter PTS.

Your understanding is very inaccurate. PTS is not a filter, it is a
property of each frame, the instant it is meant to be displayed. The
setpts filter can be used to alter the frames' PTS, resulting in changes
of video speed.

> Below are three ffprobe outputs; “Real Time”, “Slow Motion” and “Time
> Lapse”. The PTS for “Slow Motion” seems easy to detect using the PTS
> value.
> The “Real Time” and “Time Lapse” appear to have similar PTS values.

No, absolutely not. What you are seeing is the difference in frame rate:
24 fps (from NTSC, actually 24/1.001), 25 fps (from PAL) and 30 fps
(from NTSC, actually 30/1.001).

> My goal is to be able to accurately detect if a video is “Real Time”,
> “Slow Motion” or “Time Lapse” within the first 3-5 seconds of the
> video.
> I know portions of the video can change from “Real Time”, “Slow
> Motion” or “Time Lapse” and that is ok and we may classify them as
> all-the-above.
> What is the best way using ffprobe to detect if the first X seconds of
> a video is “Real Time”, “Slow Motion” or “Time Lapse”?

You cannot expect software to be able to distinguish contents that was
slowed down from contents that was slow in the first place. What you are
asking has the same kind of difficulty than https://xkcd.com/1425/'s
check whether the photo is of a bird.


  Nicolas George
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