Just serve and not transcode? Because it sounds like the Amazon Prime microservice was doing some heavy processing of uploaded video - breaking it into frames and applying some ML algorithms to them, and also the same with the audio. Sounds like even if you can fit in under the 10 min lamda execution timeout (assuming internal teams are limited to the same), that AWS Lambda/Step Functions isn't a generic job queue handler and is not infinitely parallel like AWS would want you to believe.

It's a bitl ike using an SQL database for streamed append-only logging. It'll work in test, with test amounts of data, but doesn't actually scale.