This used to work, then the author locked videos behind a pay wall. There is some paper thin excuse about how YouTube change the algorithm (True) so this can no longer provide downloads without infrastructure (false!) I don't know the actual code base, so take this with a grain of salt. However, as someone that understands video and audio encoding and containerization, this seems like bulls$h!t. There is no conceivable thing that could have changed that would make re-containerizing separate video/audio streams problematic without server infrastructure. mkv is an open standard, and there exists plenty of methods, including the browser, for repacking it on the client side. This extension is the authors ONLY project, hasn't been around for long, and doesn't do anything too novel. I suspect this was always just a coding cash grab, and we are just caught in the "capitalize" phase. Jump ship, something else will take it's place.