Right, but without the lambda infrastructure it would be infeasible from infrastructure and cost perspective to spin up, let’s say 10,000 instances, complete a 10 minute job on each of them, and then turn them off to save money, on a regular basis
You'd need some logic to shut down the instances once it's done, but the simplest logic would be to have the software do a self-destruct on the EC2 VM if it's unable to pull a video to process for X time, where X is something sensible like 5 minutes.