I’ve had the same issue for the past several months. I can provide a bit of input on this subject.
AMD Driver version 22.5.1 does not have issues with Udon Video Players. Other driver versions newer than that all show the exact problem described by the thread author ( @hero_on_vr_chat ). 22.5.1 is a WHQL-signed driver, however newer releases that are also WHQL-signed have not worked.
Driver versions I have tested personally include: 22.7.1, 22.8.1, 22.10.1, 22.10.2, 22.10.3. I have also tested the Pro drivers for Q3, with the same result.
I have not tested the latest release at time of writing (22.11.1).
My understanding of what is going on is that the way the Udon codebase calls a video player interacts with the driver to send the video data to the ASIC for video decoding, but EAC doesn’t like something about it.
EDIT: Per this post a VRchat Dev indicated it has nothing to do with EAC but does have to do with the Video Playback Library that VRchat uses, and that they have been in touch with AMD on the issue.