So I'm sure this has been tried before, but I thought I'd just throw out an example I managed to put together with free tools - in this case,
Tortoise TTS.
The script is based on an old campaign idea I had years ago, set during the Great War. The old briefing video is just a placeholder, mostly so I could upload this to youtube.
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P.S If you decide to try the demo site, try and not hug it to death (no pun intended). I've seen how much those plans cost for GPU cycles and the guy doesn't deserve a huge bill - though I wouldn't recommend doing it via CPU, because when I tried that the processing time went from 2.5 seconds or less for "This is a test" to nearly a minute.