Hi. To put the particles behind the bars adds quite a level of complexity. However, let's start from scratch: In your main comp have your video, duplicate it (Ctrl +D) and Precompose it - call it Precomp ( make sure you Move All Attributes and Open New Composition for the precompositions we're going to be doing). In Precomp add the Keylight effect and key out the green bars (toggle the Transparency Grid on at the bottom of the screen, it's the checkerboard symbol next to Active Camera). You should see a checkerboard pattern where the green used to be which shows that it is transparent. Add a new solid and make it the same green as the bars (use the eyedropper tool and sample the green from the Keylight swatch). Put the green solid below the video. You should see a TrkMat pulldown box beside the pickwhip symbol - if not press the Toggle Switches/Modes button at the very bottom of the screen and it should appear. Toggle the box open and select Alpha Inverted Matte. This will leave you with only green bars on a transparent background. Precompose Precomp - it will automatically be named Precomp 2. In Precomp 2 turn on the eyeball switch beside the video - the video will reappear. Use the pen tool and draw a wide thin box just above the top of the keyboard - this is the area that the particles will appear from. Toggle open the video layer and you will see Masks listed. Select the heading "Masks" and copy it (Ctrl +C). Select the Green Solid layer and paste the mask (Ctrl + V). Turn off the eyeball for the video layer and you should have a thin slit which the green bars will move through with a transparent background. Now, in your Main comp: make a solid and add Particular to it and move it below your video layer The layers should now be: Video Particular Precomp 2 (turn off the eyeball - make it 3D) Precomp Black Solid (you'll need to make this) Using the pen tool draw a tight mask around the keyboard only. Now go to your Particular settings and set it as per my earlier post using Precomp 2 as the Layer emitter. You should now have little green balls coming our from behind the green bars - now is the time to work on the actual particles to get them to look like you want. I've tried to be as clear as I can, if there is anything that is unclear let me know. PS: Getting some knowledge about Track Mattes is one of the most useful things you can learn in After Effects - they have a lot of uses.
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