Videos will automatically adjust quality depending on your student's internet connection. This is why you may notice that although you have a 1080p video, it might automatically play at a lower resolution. It is designed this way to ensure that your videos load quickly, which is quite common behavior with video hosting platforms. You might have noticed this with other video platforms like YouTube for example.
To give you some context behind this, videos uploaded in Thinkific are hosted with Wistia. Wistia will automatically switch quality depending on the internet speed. It makes regular checks on your student's connection and will automatically adjust the quality of the video to prevent buffering.
If Wistia detects a slower internet connection initially, and speed improves during playback, the video will start on a lower quality and then switch to a higher quality.
You can learn more about how this works here: Wistia Adaptive Streaming
If your student ever wants to increase the quality of the video they are watching, they can always use the menu options at the bottom right to select a higher resolution!