Video timelapses with FFmpeg

21 Jan 2025

An artist friend took videos of her art creation process and asked for assistance converting them into per-artwork timelapse recordings. Let’s document the steps for my future self!

Task

Trim videos to region(s) with activity—one timelapse per resultant artwork
Speed up 4x
Remove audio
Within a single recording, remove subsection(s) with no activity

For the given recordings, finding the cut points for the first and last steps could easily be done manually.¹

Prerequisite

Install commandline video editing tool FFmpeg.

Steps

After viewing a recording and making note of the timestamps around a specific artwork’s creation (in this example, 00:25:16 to 00:42:34):

# Trim into new file, remove audio
ffmpeg -i INPUT.mp4 -ss 00:25:16 -to 00:42:34 -c:v copy -c:a copy -an ARTWORK_A.mp4

# Speed it up into a 4x timelapse, update framerate=60fps, rotate 90 degrees
ffmpeg -i ARTWORK_A.mp4 -vf "setpts=PTS/4,fps=60,transpose=2" ARTWORK_A_4x.mp4

# Trim out region with inactivity (00:03:39 to 00:04:17)
ffmpeg -i ARTWORK_A_4x.mp4 -vf  "select='not(between(t,219,257))',setpts=N/FRAME_RATE/TB" ARTWORK_A_4x_trimmed.mp4

This recording happened to be filmed vertically but needed to be flipped to horizontal; if that flip isn’t necessary, exclude the transpose=2 argument from the second processing step. (For whatever reason, doing this transpose is realllllly slow. Wasn’t worth investigating here, but be warned.)
The region with inactivity was found manually (within ARTWORK_A_4x.mp4), and then converted into seconds. It could alternatively be found and excluded as part of the first step.
Note that these steps generate intermediate videos ARTWORK_A.mp4 and ARTWORK_A_4x.mp4 as well as output video ARTWORK_A_4x_trimmed.mp4. That was intentional, to give the friend the different types of output for other use-cases. If those intermediate videos aren’t desired, the various steps can be combined.

Footnotes

If the recordings were longer (or if there were more of them), I’d probably automate that step—I considered it here, because it would be fun, and then decided that it failed xkcd’s Is It Worth the Time test: ↩︎

Created: 2025-01-21
Last updated: 2025-01-21
Type: Task documentation
Tags: ffmpeg, instructions, editing, task