Video works on chrome, but not on Android App!

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For future reference, High 10 H264 video doesn't have great support with clients, so you're asking for transcoding with that type of file. It was popular with the anime community but you have to jump through some hoops to get it to work. Running an rPi as your server, I'd avoid High 10 h.264 encodes in the future, you'd have far better luck with 10-bit x265 (and maybe even AV1 honestly) as far as compatibility.