2012.05.14

Slowing down video.

Now that I’m starting to shoot some video with the Nikon D3200, I wanted to try that old trick of shooting at 60fps and then changing the footage to 24fps for a bit of slow motion action. Now, you can’t just do this by slowing down the footage, you need to conform the footage. If you’ve got Final Cut Studio 7 you can use Cinema Tools to do it, and if you have Final Cut Pro X I guess it’s even easier, but let’s pretend you don’t have those, or you prefer open source… read on!

I couldn’t find a way to conform the footage using my old pal MPEG Streamclip, so I moved on to ffmpeg, and managed to find this bit on doing a conversion with a fixed number of frames.

Here’s what worked for me with two steps. There’s a way to do it all in one shot, but I’ve not got that to work yet.

ffmpeg -i DSC_0031.mov 
  -f rawvideo 
  -b 50000000 
  -pix_fmt yuv420p 
  -vcodec rawvideo 
  -s 1280x720 
  -y DSC_0031.raw

So the first command above takes our original QuickTime file right from the camera (DSC_0031.mov) and creates a “raw” version of it we output as DSC_0031.raw (NOTE: In both examples the code should all be on one line. I’ve broken it up to multiple lines for readability. Make it one line!)

ffmpeg -i DSC_0031.raw 
  -f rawvideo 
  -pix_fmt yuv420p 
  -sameq 
  -r 23.97 
  -s 1280x720  
  -y DSC_0031-24fps.mov  

Once we have the DSC_0031.raw file complete, we run the second command and create a new file named DSC_0031-24fps.mov, which will now be at 24fps instead of the original 60fps. Note that we also specify the resolution (1280×720) and the frames per second (23.97). Obviously if you want other values, change those to something else.

So here’s the final video, shot at 60fps and played back at 24fps for just a little bit of slow motion. (With the RED ONE We can shoot at 120fps, but hey, a cheap DSLR doing 60fps isn’t too bad.)

One more thing on the video, it was shot with 3 camera angles, but only one camera. The trick here is to shoot the same sequence 3 times (yes, I drilled 3 boxes) with the camera in a different position each time. We do this all the time, sometimes you have to when it’s a one camera shoot, and sometimes it just works out based on the footage you’ve got.

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