Blog . How to Use a Mask to Erase in After Effects
Step 1: Open up Adobe After Effects and select the New Composition option in the window that appears.
Step 2: Now another window will appear and it will let you choose how long your video will be, along with other options for your video settings.
Step 3: Once your new composition is open, go to “File” and select “Import”. This will allow you to bring in any files that you want to work with.
Step 4: When your files are all imported, drag them down to the “Animation” window at the bottom of the After Effects Window.
Step 5: With all of your files in the correct window you can start to edit them. I brought in nine videos I made and will make a pattern out of them. All nine videos I imported are of a video I made previously. I trimmed all videos to show only a sphere of imagery.
Step 6: To erase a video in After Effects is easy, but will take a long time to render. If you are like me and have a simple shape that you want to erase the background of, it is much quicker to use a mask.
Step 7: In order to make a mask you must select the “Mask” tool from the toolbar at the top. Once it is selected, click and drag the cursor to make your mask.
Step 8: Once the mask is made it will get rid of everything except for what's inside of it, erasing any unwanted video.
Step 9: You should now have a shape without any video other than what’s inside the mask. To make sure the video you wanted to get rid of is gone, you can make the video background transparent by selecting the checkered box at the bottom of the screen.