Switch to offering a year of free updates and charge a small fee after that.
Trust me. You will coverge to this scheme sooner or later, so do it now.
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Standalone Windows installer is a must.Windows Store is still a deserted wasteland and is not a default choice for the vast majority of Windows users. You are losing a ton of users over this.
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ffmpeg and other dependencies need to be acknowledged for both ethical and technical reasons. The technical reason is that your app doesn't depend on OS-supplied codecs and doesn't require installing them separately. And ethical reasons I hope are obvious.