A title can have several editions
Read the viewing offer for the resolution supplied with that edition. A 4K television does not make every film available in 4K, and a sharp catalog image is not a measurement of the video stream.
Choose stability as well as detail
If a player repeatedly buffers, try a lower quality setting when available. A stable HD picture may be more enjoyable than a higher setting that cannot keep playing. Adaptive players can change quality as network conditions vary, so a briefly soft opening image does not always mean a lasting problem.
Check the whole combination
The viewing service, plan, title, app and device can all affect available quality. Follow the service's own requirements for high-resolution playback. SubsMovies opens the viewing choices but does not control the external player's resolution or delivery.