how to blur multiple images and faces in same shot

Use a Gaussian blur filter.

Add a Shape mask for every face you want to blur. (When you mouse over the Effect name "plate", the Add Mask icon will appear. There is an option for a Color mask as well... you won't need that here.)

Go to the beginning of the clip and Set a keyframe on each mask.

A fast way to "track" is to Shift - right arrow (double or triple tap is usually good enough for smooth motions) through the clip and reposition the masks as necessary.

Almost all Effects have this option available (except a few specialized effects like the Keyer, Luma keyer, and Apple supplied Masks.)

Grab it from the Effects browser and drag-drop it on your clip. Once you've done that, a panel (as in the attached image) will appear in the Video inspector in the Effects section (top of the list). You will start there and mouse over "Gaussian" and where the mask icon appears, click on it and Select Add Shape Mask from the popup menu. To add a keyframe, mouse over the "Shape Mask" layer that appears at the bottom of the pane and a yellow diamond shape will appear - click on that diamond to initiate keyframing. Move the playhead to different times (use the shift-right arrow to advance the playhead 10 frames at a time) and all you need to do is grab the shape's control in the view to a new position. Any changes in the shape's size and shape (circular, oval, rectangular, etc.) are also recorded as keyframed changes. You can pretty much add as many shape masks as you need. The "active mask" for editing will have an onscreen control. You activate any mask in the viewer by clicking on either the layer in the inspector, or inside the area of the shape mask in the viewer (if any of them are already selected in the viewer).

The default mask is a circle. You can change the size by clicking anywhere on the "path" and dragging to a new size. There is also a "feather ring" that operates the same way. The difference between the two paths is the actual bounds have green dots on the path to control the size. There is also a small white circle near the top center. Dragging on this control will change the shape from a circle to a rectangle or round rectangles "in between" the extremes.

You should have a relatively easy time adapting to the interface. And like I said earlier, this feature is available on almost every Effect in FCPX (it was previously exclusive to the Color board/Color Correction effect.) So, if you'd like to use a different blurring effect, take your pick.

mayqlaf wrote:

Another question. Sometimes I apply the filter to the clip and when I go to replay it, the filter isn't in effect, or in an entirely different place than where I put it.

Nick

Try this:

Move the Playhead over the desired clip.

Select the clip, to confirm you see a yellow border.

Next, move the cursor over the desired Effect.

The yellow border around the clip will turn white and the Effect Thumbnail will match the clip.

Double click the Effect Thumbnail and that effect is added to the selected clip.

An instance of the Effect is added in the inspector.

If you double click the Censor Effect again another instance is added and so forth.

Al

LLook at the image. The effect is applied to the clip three times. Drag the effect from the browser onto the clip however many times you need. Select each effect in the inspector and you have separate controls for it.

AS I said you drag the effect from the effects browser onto the clip in the timeline three times or however times you need. Or you do what fox said use the shape mask multiple times on the Gaussian effect.

This cutting of holes into the bottom layer would have been simpler than all other solutions mentioned except, of course, for simply dragging the filter onto the flip multiple times. Or duplicating the filter multiple times. Or copying and pasting the filter multiple times. all of which work for me.

You can apply Censor multiple times. I've applied it three times in this image

IN the olden days we duplicated the layer and stacked them, blurred the bottom layer, and then cut mattes with soft edges through to the lower layer.