We will need to animate the Active property of the Core Flare for the Gunfire effect to make the muzzle flash appear and disappear in quick succession. Open up the Core Flares tab for the effect and click on the little circle to the left of the Active property.

This will turn the circle green, indicating that keyframing is enabled for this property. Since I move my gun throughout the shot, we also need to animate the position and orientation of the muzzle flash, so enable keyframes for those properties as well. The circles next to all of these properties should now appear green as shown in the following screenshot:

Expand the Gunfire layer in the composite shot to reveal all of its properties in the timeline window. Scroll down until you find the Active property on the left side of the window. Then move through your clip frame by frame and tick or untick the Active checkbox to only show the Gunfire effect for the frames in which you are shooting your gun. We want the muzzle flash to only ever be active for a single frame before vanishing again.

You should see little grey diamonds appear on the timeline as you do this, indicating the new keyframes you are creating. Note that you can select, copy and paste these keyframes on the timeline window to make this a little quicker for you.

Next, step through the composite shot again and visit only the frames in which the Gunfire effect is visible. For all of those frames, reposition the muzzle flash effect correctly at the tip of the gun, aimed in the right direction. In my clip, I swing my gun around a little bit so I want to make sure the Gunfire follows that movement and is shooting straight out of the gun each time. This is where the 3D properties of the effect in HitFilm 2 comes in very handy – doing this realistically with flat, 2 dimensional stock footage would be very tricky.

And we’re done with the muzzle flash effect. The gunfire should now shoot realistically out of the gun in quick succession.

Now it’s time to add some fake lighting to the effect so it looks as if the Gunfire actually illuminates the surrounding objects.