Not impossible, but for the case of Beavis and Butthead, you’d need tight control over the start/stop timing, the ability to choose a specific version of the vi

Not impossible, but for the case of Beavis and Butthead, you’d need tight control over the start/stop timing, the ability to choose a specific version of the video (can’t have some newer one with extra stuff added or some cut or whatever, even just blank space at the beginning or end), the ability to cut away from the video while the audio continues and mix in your own extra audio, all kinds of things like that. It’d be a lot of complexity when you could just… bake it in, which also tends to be the best way to preserve anything, simply connecting all the relevant parts together (practically) inseparably (see: link rot).