Bug#956640: Here's how to fix this issue

patch via ungoogled-chromium and Fedora. Refactor debian/patches/fixes/gl.patch to make the changed line read + glx_image_ = new gl::GLImageGLX(size_, gfx::BufferFormat::BGRX_); And rebuild. Proof of concept here: https://build.opensuse.org/package/show/home:stevenpusser:schmonium/chromium

Bug#956640: Confirmed with a personal backport of this version to Buster.

It's not just streaming video--it also is messed up with any videos, including local files, that try to use va-api. Videos that aren't supported by va-api on my laptop, such as the newer AV1, look just fine.