There was an old, locked topic that touched on this but it isn't quite accurate or complete. And a search using any of the terms in this topic's title comes up dry. So I'm posting this new one topic in the hope that people will be able to find this helpful tip.
The Mbps required for uninterrupted streaming is dependent on the quality of the program. One component of this is the bit rate. There is a hidden Bit-Rate Override menu that allows you to change your Roku's bit rate from Automatic (stream at the highest possible quality) to a specific rate. You can select from one of the following streaming speeds (Mbps) (which changes your Roku to a corresponding bit rate): 3.5, 3.0, 2.5, 2.0, 1.5, 1.2, 1.0, 0.6, and 0.3.
If you don't have a high-speed Internet connection, you may want to change from Automatic to a lower speed that is more compatible with your network. By selecting a lower speed, you can reduce – or even eliminate – the program interruptions that occur each time the buffer needs to be replenished.
To get to the hidden Bit-Rate Override menu, you need to enter the following key sequence on your Roku remote:
On the screen that comes up, you can limit the speed (program quality) at which Roku will try to stream programs.
You might find that, even at one of the lower speeds, the quality difference could be minimal but the buffering interruptions will be much more tolerable or completely eliminated.
At the bottom of Bit-Rate Override menu there is also an Enable Playback Debugging option. The Enable Playback Debugging option which will display download information each time a program is streamed. An example of the message displayed is "Playing 2.0 mbps stream on your 2.6 mbps network." From this debugging window you can learn a lot about the programs you are trying to stream as well as the speed of your connection ... especially the connection side of the equation. You will probably find that your network's mbps can vary widely and this will give you a clue as to what bit-rate (Mbps) setting should give you a tolerable number of interruptions. Once you think you've determined a suitable speed, you can return to the menu and select a speed to try for a while.
(In fact, I implemented the bitrate override screen and the underlying functionality.)
If the channel provides multiple nonadaptive streams at different bitrates, the firmware should pick a stream that matches your network bandwidth. If the channel only provides streams that are faster than your network, then changing the target bitrate isn't going to help anyway, since there's no stream that you can play. The only time it will help is when your network bandwidth fluctuates significantly, so that the firmware doesn't have a good idea of your actual bandwidth at the time you start the stream.