User Manual

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❖ Some corporate and institutional network administrators opt to support one or another format
exclusively. (Check with your IT department to find out if this affects your decision).
❖ RTMP and RTSP combined have a very wide installed user base, and work well across multiple
platforms (PCs, Macs, Linux, etc.).
BANDWIDTH CONSIDERATIONS
You’ll often hear the term ‘bitrate’ in connection with streaming. 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 streaming Profile setting in
the system’s Configuration panels. 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 connections 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 at the specified bitrate, 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 18.8.1 for some useful resources.)
18.6.2 STREAMING MEDIA PROVIDERS
Using a commercial streaming media provider (sometimes referred to as a Content Delivery Network, or
simply ‘CDN’) bypasses otherwise high-bandwidth requirements for the encoding computer. When you have
made arrangements for a streaming media provider to distribute your stream, the encoder only needs
enough bandwidth to get a single a/v stream to the provider. All end users connect to the provider to view
the stream.
Most streaming providers have access to massive bandwidth (and often, with very little notice, they can scale
up your allotment to meet a temporary need.) Since your local bandwidth is really only used for uploading
a single stream, you can send a high quality stream, secure in the knowledge that it will not degrade as soon
as a second viewer attempts to see it.