When we hook up our Internet TV box for the first time, we are allowed – in most cases – to set our TV resolution to 1080p. But the reality today is, that this resolution does not by itself state the picture quality.
Such video streams are sent to the receiver in compressed format, and the compressed bit-rate is a more accurate indication of what the actual picture quality will be. I.e., even if the basic format is 1920×1080, by compressing the stream more, lower bit-rates can be achieved, at the expense of picture quality.
Modern Internet TV boxes are quite intelligently programmed, to be able to change the bit-rate in mid-stream. Thus, when my ‘Roku‘ started buffering, during an initial test, it did not only allow for its buffer to catch up with the point in the movie I was watching, but also noted that the real bit-rate of my connection was not high enough to support the highest quality level, available at 1080p. Immediately after that, the picture seemed slightly less sharp, but as I continued to watch, the overall quality of the picture started to recover again.
My Roku has never had a streaming-interruption since then.
In fact, the way it is with HDMI connections to our TV, it is impractical for the source of the stream to change the picture-format in mid-stream. It tends to stay fixed.
And when we compare Bell Fibe – which is a service offered by my ISP, also to stream TV to me via DSL – its reason for maintaining a consistent picture-quality is actually different. In this case, the bit-rate of the Fibe stream is reserved at the Modem / Router, which also belongs to Bell. I.e., the Bell Modem can ensure that a certain rate of bits per second are available for TV, and can do so at the expense of actual computers also trying to communicate. My Roku is counted by the Bell Modem, as just another connected WiFi client.
What this actually means, is that if another person is considering buying a Roku, but worried that his Internet is not fast enough – as long as he does have some form of high-speed Internet – he need not worry much. The receiver would detect his slow connection, and adjust the picture quality to suit.
Also, with a Roku, we get to set the picture format to 720p instead, so that the required bit-rates start at a slower one.
If my TV was a 4K TV, I could set the format accordingly, but then I would worry, that this might be time and money wasted, because then, the picture quality on my network might not keep up with the 4K format.