The service was limited to 480p (standard definition), matching the Wii's maximum output.
While you cannot currently stream movies on the device, the following details outline how the service originally functioned and why it is now unavailable. The History of Netflix on Wii How To Netflix On Wii Console
Support officially ended alongside the closure of the Wii Shop Channel. Why Netflix No Longer Works Netflix Streaming Comes To Wii - Game Developer The service was limited to 480p (standard definition),