NewTek TriCaster 855 - Manual (Page 264)

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BANDWIDTH CONSIDERATIONS
You’ll often hear the term ‘bitrate’ in connection with streaming video. This expression refers to
data throughput per second (generally measured in Kilobits per second, or Kbps.) You could
think of this as being like water flowing through a hose. You control the ‘faucet’, because you get
to choose the Stream Profile in TriCaster’s Stream Configuration panel. However, you don’t own
the ‘hose’ – or at least, not the entire hose.
Once the stream leaves your immediate environment, even if you can supply good throughput
locally, bandwidth may be constricted elsewhere along the transmission path. The level of
Internet traffic can impose limits, but another major factor is the sort of connection your viewing
audience may have.
Consider an example scenario: Even though you know that most of your audience is going to
connect to your program using (relatively slow) wireless devices, you use a very high outgoing
bitrate – thinking that this will surely be enough to fill the need. The fact is, though, a high bitrate
actually ensures their experience will be poor!
The client player tries to play the stream at the bitrate you specified, but (in this example) the
wireless bottleneck impedes flow. It is as if you connected a fire hose on your end, giving them a
suitable high capacity nozzle for their end – but in the last stage of flow, the stream must pass
through a small garden hose. Sadly, the stream will be quite insufficient, and output from the
‘nozzle’ (the client player) will falter badly.
For reliable performance, try to ensure the potential upload bandwidth from your system to the
net is around twice the bitrate you choose. You can broadcast at a rate closer to your actual
ceiling, but reliable performance cherishes headroom.
Also consider the expected download abilities of your viewers. Ideally, a safety margin 1.5 times
the stream’s bitrate is desirable. This may mean you need to consider using a lower resolution,
or lower framerate for your stream – but doing so when required will generally deliver a smooth
result, and is the wise course. (Nothing inclines viewers to turn away quicker than a stuttering,
start and stop stream. See “Speed Tests” in Section 15.8.1 for some useful resources.)