Test the broadband where you watch TV
Measure at the screen you use and at the time you watch. An advertised broadband speed describes the package, while a test by the TV gives you a better starting point for diagnosing playback.
Use two tests with one change
Run a speed test near the TV, then test from the same spot with other household traffic running as usual. If you can connect the player by Ethernet, repeat with the same programme and compare the results. A useful comparison holds the programme and device steady.
Use a benchmark from the service you watch
Netflix publishes 3 Mbps for 720p, 5 Mbps for 1080p and 15 Mbps for 4K. These are Netflix recommendations. The requirements of another player or stream can differ, and another screen, game download or cloud backup will use some of the same connection.
Write down what changed
If the same programme plays well on a cable but stops on Wi-Fi, move the Wi-Fi test closer to the router before changing a subscription. If only one programme fails on both connections, collect its name and time for support.