When I connect my laptop via HDMI to my TV laggt the video. How so?
Because your computer does not have the picture on z.b. 15 inches must be expected but on z.b. 51 inches that lasts.
If he's not fluent, just let preload briefly and then play.
If you stream the film can also be at your internet connection.
When streaming, it may also be that the provider blocks the output via HDMI
This has nothing to do with the size of the screen. Most laptops can spend up to 1080p. The number of pixels on the screen or TV does not say anything about the resolution (for example, does my 10 inch tablet have a resolution of 1920x1200, the slightly larger 22 "TV" only "1920x1080 pixels).
A UHD TV will give a laptop a corresponding signal only if the laptop controls it and in this case it will also have the necessary power. In the other case, the TV calculates the signal high.