New to the program, running on a Lenovo Thinkpad, Windows 10, 64-bit version of Purr-Data (most recent). I am simply trying to play a video (AVI). I can create the window, open the file, see the video file show up in the window, but it does not play. When I toggle auto, the program crashes, forcing me to quit.
One recommendation is to install the K-Lite Codec Pack -- I can't find a direct link on this machine (regional search restrictions -- I can find "uptodown" style links but I don't trust them) but it should be easy to search. Gem depends on the codecs available on your system. If one fails, another might be successful.
With that said, though... it's with some regret that I have to say that the state of the art for graphics passed Gem by quite some time ago. I still use it in class because the students just need a basic smattering and it's good to stay within the Pd paradigm, but it's far less advanced than Jitter in Max/MSP ($) or vvvv (Windows only I believe, so you're in luck there -- free for noncommercial use) or Processing.
In Pd, there's also Ofelia, but get ready to write Lua code into the objects. It's much more performant than Gem but a lot harder to use.
PS There's a rant in there somewhere about that user handle but I haven't got energy for it now...