Playing with video editing

When I was a kid, at the dawn of the TV era, there were two Australian TV imports that I liked to watch: Skippy the Bush Kangaroo and The Magic Boomerang.

In The Magic Boomerang, a young kid, has a boomerang that stops time when he throws it. The plot always involved some crisis that the lad was able to sort out by stopping time for the 20 seconds or so that the boomerang was in flight. Though everything else stood still, he was able to carry on as normal in the temporarily time-frozen world of the Aussie outback. This was the first time I’d seen time manipulated visually in this way.

More recently the BBC discovered video compositing and there’s hardly a news or current affairs programme that doesn’t involve a presenter standing in front of a time-accelerated high street. A similar technique, this time slowing down and stopping time, was used to good effect in the last series of Hustle, predated by Hiro Nakamura’s time-stopping tricks in Heroes.

It’s easier than it looks to do this and I’ll demonstrate two effects ­ one accelerating time and the other stopping it, both including a person in the scene, for whom time passes normally.

Matting
Both effects rely on a technique called matting. In Adobe Premiere Elements 7, which I’m using here, it’s called a track matte, and other applications call it a travel matte. Mattes are used to hide parts of a video track and reveal video in underlying tracks. Mattes can be animated and can be video clips. We’ll be using a simple static matte that splits the screen into two areas, one in which the action occurs in real time and the other in which time passes more rapidly, slows down, or stops.

The first effect shows a real-time individual in front of a street scene in which time is accelerated. You’ll need the camera on a tripod positioned so your presenter is in front of a static backdrop that extends part way into the scene. By ensuring that what’s behind the presenter remains static, compositing the real-time section with the fast-motion street section is much more straightforward.

Next, shoot the presenter’s piece to camera as normal. In this example we’ll assume the length of the piece is 10 seconds. When you’ve got what you need, keep shooting ­ your presenter doesn’t need to be in shot for this bit. How much additional footage you need will depend on the length of the finished piece and how much you want to speed things up. To get the effect of time passing rapidly ­ with cars and people zipping around and clouds whizzing overhead, you’ll need to accelerate the action by around 10 times or more, so for a 10-second finished piece you’ll need 100 seconds, or nearly two minutes of real-time footage.

Capture the footage and divide it into two clips ­ the 10-second ‘to-camera’ piece and the two-minute background scene. I’m doing this in Adobe Premiere Elements 7, but most other video editors will handle it in a similar way. The minimum requirements are multiple video tracks, matting ability and speed control.

Stretching time
In Premiere Elements 7, drag the two-minute background clip to the video 1 track. Select the Time Stretch tool above the timeline then select right end of the clip and drag it leftwards until the clip is only 10 seconds long. The 1,000 per cent speed increase is shown in brackets on the clip. You don’t want the speeded up audio on this clip, so first uncouple it from the video by right-clicking the clip on the timeline and selecting Unlink Audio and Video from the context menu, then select and delete the audio clip.

By default Premiere Elements 7 creates three empty video tracks in a new project, which is the number you need. Beware if you’ve deleted and then added new tracks as a bug can cause matting to fail in these circumstances. Drag and drop the 10-second presenter clip into the Video 2 track.