SubscribeIt’s not obvious how to change the speed of a Quicktime playing in Quartz Composer and it’s even harder to smoothly change speed to allow “video scratching” style effects.
There’s a few tricks involved. First you must change the quicktime or composition to external timebase by right clicking on the node or macro and selecting it from the pop up menu. Second to smoothly scale the speed you must use a combination of a patch time node and a javascript that scales the running patch time smoothly. Last thing is that there is currently a bug in Quartz Composer, the first time the composition is played the javascript fails with a “NaN” error. Stop the composition and restart it and it works correctly. At present I don’t know of any way around this.
A very cool thing is that you can build a composition as complicated as you want with all sorts of LFO’s or random movement then put it in a macro, enable external timebase and control the speed of the whole thing. There are many possibilities for syncing to midi timebase or BPM using this.
The screenshots show the details and you can download the quartz patch “speed_with_timebase” to build on yourself.
Technorati Tags: Quartz Composer, VJ
> javascript fails with a “NaN� error
hope this helps.
—
var prevScaledTime = outputs[0];
var speed = Number( inputs[0] );
var dummy = Number( inputs[1] );
if( prevScaledTime == undefined )
{
prevScaledTime = 0.0;
outputs[0] = 0.0;
}
else
{
outputs[0] = prevScaledTime + speed/100.0 + dummy*0.0;
}
Left by qcjp on August 4th, 2005