We have done some testing in debug. Below are our findings. As you can see it is clear that there is something going on that is not due to network bandwidth going down. As I have specified the stream server and roku are in the same network, and this behavior happens with other channels live streams as well.
Software: 2.9 - build 1529
Hardware version: model N1101
Serial number : D0D029016644
Network: roku + streaming server
Speedtest: download -> 37222; upload -> 39956
Roku with playback debug enabled:
FIRST TESTS ON OUR PRIVATE CHANNEL
Max speed: 10 mbps when powering Roku
The speed decreases in time after playing live streams: 5.6 mbps, 1.2 mbps, 0.8 mbps
If the HLS bandwidth is set to 932 and Roku calculates the network bandwidth lower than 0.9:
Debug message: Cannot play 0.9 mbps stream on your 0.5 -> 0.9 mbps network because starting at 5:30 the stream needs 0.7 mbsp in the next 6 seconds (0.9 mbps).
If the HLS bandwidth is set to 640 and Roku calculates the network bandwidth greater than 0.6 (eg: 0.8-) : the stream plays instantly
OTHER TESTS ON Spacevidcast and OUR CHANNEL
19:10 -> 10 mbps
19:15 -> cannot play 0.8 mbps stream on your 0.6 mbps network because starting at 1:28, the streams needs ...
19:16 -> 1.1, 1.3 mbps
loading, please wait -> makes buffer when playing and stays a lot (more than 5 minutes - it doesn't start again)
19:22 -> cannot play ... on your 0.1 mbps network
19:23 -> cannot play ... on your 0.2 mbps network ... 0.3 mbps
19:24 -> cannot play ... on your 0.4 mbps network
19:25 -> 1mbps -> plays instantly
19:30 -> 0.7 mbps
19:34 -> 1.1 mbps
Starting from a difference of 0.1 mbps between the bandwidth needed by the stream and the network calculated bandwidth the stream stays longer on the buffering phase (eg: 0.6 (or lower) mpbs stream on your 0.7 mbps network)
--reset ROKU --
19:48 -> 10mbps
19:48 -> 10mbps
19:53 -> Cannot play 0.6 mbps on your 0.7 mbps network
19:40 -> Cannot play 0.6 mbps on your 0.7 mbps network
19:41 -> 0.8 mbps
19:56 -> Cannot play 0.3 mbps on your 0.7 mbps network
When powering/reseting ROKU the speed is 10mbps.
After playing some live streams the speed decreases. When it calculates the network bandwidth as beeing with 0.1 greater than the stream bandwidth, or lower the buffer time is longer.
The network speed eventually increases again and decreases again but not very significantly.