Calculates total length of videos in current folder. It was a nice exercise, and also a lesson - AVOID USING NATIVE LIBRARIES if you want to make a cross-platform program in .NET Core. The platform detection code should work fine, feel free to use it for some of your projects.

Usage: Run it from the command line, it will calculate the length of all videos in the current folder. You can also specify the -r argument which will also make it scan subdirectories. (recursive)