Can you control the speed of a video clip playing in Quartz Composer?

Question

Is there a way to manipulate the speed of the video playback? I'm especially interested in a way to slow down with frame blending, exactly like the function in Final Cut Pro.

Answer 1

Interpolation should be able to help you. There's an example included with Quartz Composer (Interpolation Modes.qtz) and a beginning tutorial here that breifly mentions it (step 5). this wiki article also discusses it and talks about the different types.

Note: I don't actually have a Mac that can run QC, so this is just what I've been able to find through Google, but it sounds like it should get you on the right track.

Answer 2

Currently it's not possible to do frame-blending using the built-in Movie Loader patch.

You can arbitrarily control the playback head, though.

• Insert a Movie Loader patch, and set the Movie Location.
• Connect it to a Billboard. The movie should play at normal speed.
• Right-click on the patch, select Timebase, and then select External. This gives the Movie Loader patch a Patch Time input, and freezes it at the first frame.
  • The value you enter for Patch Time is the time offset, in seconds, at which the Movie Loader should render.
• Insert a Patch Time patch, and connect its output to the Movie Loader's Patch Time input. The movie should again play at normal speed.

Now comes the fun part:

• Insert a Mathematical Expression patch and enter t/2 for the equation.
• Connect the Patch Time patch to the input of the Mathematical Expression, and the output of the Mathematical Expression to the Patch Time input of the Movie Loader patch --- the movie now plays at half speed.

You can alter the equation to change the playback rate --- t/3 will play at 1/3 speed, t*2 will play at double speed, and so forth.

However, if you change the playback rate equation while the movie's playing, you'll notice that the playback head jumps to a new position rather than continuing on from the previous time.

To solve this, you'll want to use the Integrator patch.

• Create an Integrator, set the Value to 1, and connect the Integrator's output to the Movie Loader's Patch Time input. The movie should play from the beginning at normal speed.
• Change the Integrator's Value to 0.5. The movie should play at half speed, continuing from the current position.

You can even play movies backwards using this technique (though, depending on what codec you use, it may severely impact performance).