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Slowing Down Movies in Quicktime

Just a quick post today.. Awhile ago I was putting together some video screencasts, and needed a way to “slow-down” the video to play certain sections at half-speed. After much trial and fiddling, here are the steps that actually worked to produce a saved copy of the movie (not just run the slow motion effect on the live movie).

Slow down Quicktime movie (play at half speed)

To slow down a quicktime movie to 50% of its original speed (and save a copy of it), the trick is to add the scaled video to a longer audio file. Here are the basic steps:

  1. Open both files (the scaled video and the longer audio).
  2. Switch to the video file you wish to turn to “slo mo”.
  3. Select all (Command-A) and Copy (Command-C).
  4. Switch to the audio only file.
  5. Select all (Command-A).
  6. Choose “Add to Selection & Scale” (Edit menu).
  7. Open the Movie Properties window and single click on the Video track.
  8. Choose “Extract” (upper left of the window).
  9. Use “Save As” to make a new copy of this “slo mo” video track.

To match up the durations of the audio and video files, just remember that half-speed video requires a audio file that is twice the duration of the original video track. I.e., 30fps becomes 15fps in the combined slo-mo file. This technique works in general for slowing down and speeding up video tracks.

Better way?

I grabbed this technique from here.. it seemed like the only thing that would work, but in my experience there is almost always a better way.. if you happen to know one, please share in the comments. Thanks!

Jeff Starr
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Jeff Starr = Fullstack Developer. Book Author. Teacher. Human Being.
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Perishable Press is operated by Jeff Starr, a professional web developer and book author with two decades of experience. Here you will find posts about web development, WordPress, security, and more »
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