The fire wipes were part of a stock footage library I purchased from www.vce.com. It's a reasonably priced collection ($250 for 4 CDs) but I've only found a few usefull shots in the entire collection. However, compared to Artbeat prices, if it has one useful shot it's worth the $250.
On the CD the wipes existed as pict sequences with an alpha channel. To use them in Final Cut, I converted them to dv quicktimes in commotion, but After Effects would work the same. During the conversion I saved two versions: One of the fire alone without any alpha, and one of the supplied alpha as straight video. The two dv files looked like this.. of course without the blue arrows and stuff:
And my final cut timeline:
In Final Cut, I started with my outgoing video on V1. In this case it's the pre-rendered Freako Title card that Dave gave me called "title1.dv" - we'll call this A. On V2 is the alpha I converted. It's just black and white. It's a straight alpha, not one that's imbedded as an extra track in a quicktime file. Notice that I sped it up to make it wipe faster. Next on V3 is the incoming video, which is my shot of Ernesto - B.
First let's just cover the wipe without the fire.. these 3 video layers have that going on. To use an straight alpha in FCP, you use the Composite Mode under the Modify menu. First select the video segment in the timeline, then choose the desired composite mode from the menu. You also have to make sure the tracks are in the correct order. The Background (A) goes a the bottom (my outgoing video), then the alpha above that, then the foreground (B) above that.
The next step is to set the composite mode on the Foreground or Incoming video (V3) to "Travel Matte-Luma". This means that it will use the luminance value of the next level down to determine what part of the picture will be pulled from the foreground (B on V3) and what part will be pulled from the background (A on V1). So in this case, the next level down (V2) is our alpha.. everything black will be background, everything white will be foreground. Since the alpha wipes from black to white, the result will be a shape wipe from video A to video B.
If you it this and find that the wrong picture is on the wrong side of the wipe, simply Channel Invert the alpha so that black and white are swapped. In my case I had to do this.
If your composite is not clean, meaning that you can see some bleed of two images. That means that your alpha white is not white enough and the black is not black enough. Again, just modify the alpha within fcp using a video filter. Image Control - Levels, or Brightness and Contrast to fix that. Just experiment.
Next.. the fire. The fire was placed above everything on V4. Since I sped up the alpha I also sped up the fire by the same amount to keep them in sync. Of course, I desaturated the fire to make it black and white using a video filter. Then, to composite it, rather than trying to key the fire on, I simply added it to the picture using Composite Mode - Add. Fortunately this works really well with fire and light in black and white.
If the shot had been in color I would have experimented to find what looked the best. Possibly still just using Add. Or maybe using a combination of adding and keying to get the best look.
The last thing to note is that once the effect is over, I moved my incoming video (B) down to V1 because in 2 seconds it's going to be fire wiped again. Otherwise my video layers would keep going up and up and up.
- By David Hartman.