Professional encoders who fully understand the encoders and the schemes in use and care about not seeing artifacting or low quality would never intentionally go as low as 300mb for a feature length movie of even an hour. Yes there are people who do such things but they’re not well regarded and it won’t look even passable on anything larger than a phone screen.
This has not been well regarded since the days when DivX ruled the pirate scene, and even then cramming a film onto a 600MB CD left a lot to be desired.