This problem still exists in Unity 2021.2.18f1, using the video player component, setting the render mode to “material override”, and material property to “_EmissiveColorMap” will not show the video even though the render texture has been assigned to the material instance. After some digging, creating a small script and put it next to the video player component should fix the issue.
void Start()
{
GetComponent<Renderer>().materials[matIndex].EnableKeyword("_EMISSIVE_COLOR_MAP");
}
related thread: Adjusting Emission Intensity of a material with the HDRP Lit shader at runtime not working