[Mike Clasby]

Short Answer, Auto Trace to get one mask of your “audio wave effect” and the area below.

I don’t know how you’re making your “”audio wave effect” on the screen that animates, stretching from the left side of the screen to the right,”. I used Render>AudiovSpectrum (Analog Lines) stretched from left to right. I then added an open mask, four points with the Pen Tool. The Mask is shaped like a bucket with the Audio Spectrum as a lid on that open bucket. Make sure the bucket overlaps the lid. Also make the bucket bigger than the bottom of the frame, meaning the mask points are outside the screen, so Fill will fill the whole bottom of the screen.I added stroke to the bucket mask.

Then, Layer>Auto-Trace (Time Span=Work Area, Tolerance and Threshold at 1) to get masks of the shape of the bucket and lid.

I got two masks on a new Auto-Trace layer, one for the inside, one for the outside. I deleted the inner mask, Mask 2, then Applied the Fill Effect (Render>Fill on AE6.5). Choose the color you want.

[Mike Clasby]

There are a lot of Public Domain films here:

https://www.archive.org/index.php

Drill down into Moving Images. There are Feature Films, Cartoons, Educational Films, Army Training Films, Newsreels, and more. It’s not all Public Domain so check each section.

[Mike Clasby]

Does this do what you want, tweaked to your case, of course?

https://www.creativecow.net/articles/lee_james/particle_build_up/index.html

[Mike Clasby]

Fire, tuts and tips on compositiong there too.

https://www.detonationfilms.com/UnitK-8.html

There are more pages and freebies on the detonation site.

[Mike Clasby]

Fire

https://www.detonationfilms.com/UnitK-8.html

There are more pages and freebies on the detonation site.

[Mike Clasby]

Andrew, aka The Master of Mayhem, has tuts and sells gory stuff galore on his site:

https://www.videocopilot.net/

For some freebies (the free downloads) and more to buy, cheap, try this:
Blood
https://www.detonationfilms.com/UnitK.htm

There are more pages and freebies on the detonation site.

[Mike Clasby]

Andrew, aka The Master of Mayhem, has tuts and sells gory stuff galore on his site:

https://www.videocopilot.net/

For some freebies (the free downloads) and more to buy, cheap, try this:

https://www.detonationfilms.com/UnitK.htm

There are more pages and freebies on the detonation site.

[Mike Clasby]

Not quick, but select the layer, “I” for in point, check the “Add or remove keyframe at current time” box (next to the eyeball), then select the previous keyframe, right click>Select Previous keyframes and hit the Delete Key.

[Mike Clasby]

My favorites for stills. Most are Public Domain but check each page/site for details.

https://images.fws.gov/

https://www.nps.gov/archive/yell/slidefile/index.htm

https://www.photolib.noaa.gov/brs/clind1.htm

https://www.usa.gov/Topics/Graphics.shtml

[Mike Clasby]

Yep, with Da Script:

https://del.icio.us/escruz/Rotoscope

It was written for Roto, but will attach mask vertices to trackers for any purpose. It works as good as the track.