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Thoughts from our SRT Broadcast: Part 3

Today, I'm going to jump back to do Part 3 of our 5-part analysis from our broadcast using SRT as a transport last month.


The discussion today will revolve around how we determine settings for the best possible SRT stream to our studio. Mind you, this is still in development...


Setting up an SRT Stream


So there are a few factors that go into setting up an SRT stream we have found that makes it effective.


1) Your Real TIme Transport

2) Your Maximum Bandwidth for Upload

3) Your Packet Loss on your network/connection


These three things we get from using our point-to-point ping test app. So first you must just do a general speed test, so you know the speed you have available.


A thing to note on this, if your upload is higher than your download, use the speed provided for download. If your download is higher than your upload, use the upload speed. These actions will give you the correct bandwidth you need.


Next, we go and do an advanced ping test to the IP of our studio. What this does, since we are using point-to-point, is it gives us the near actual latency and packet loss that occurs.


With this data, we input it to a spreadsheet I am currently developing to determine the stream setup.


So when we have a RTT (Ping) number (in this case 221 ms) we enter that into the RTT field. For this we use the maximum amount of latency experienced in 16 packets sent to our server.


With the packet loss number, we enter the packet loss result of the tests. With that, we can determine our overhead and RTT Multiplier.


The final number we enter is our bandwidth which is taken with our test of our upload speed which was extremely low, at 0.12 MBps.


Using known formulas to calculate the numbers:


Latency = RTT x RTT Multiplier

Channel (Pipeline available) = Bandwidth x 1+overhead

Bitrate (Average Rate of Broadcast) = Channel x 75%


With these numbers, you will be able to do a broadcast.


NOTE: In this particular setup, there is extra work to do to ensure that you have a smooth looking production due to the fact that the speeds available are so terrible. In our initial test run with SRT, our bandwidth was around 1 MBps which makes a stream possibilities much more workable. At the rates in this example, you need a high end encoder where you can setup a stream in the same bitrates. Apps like Larix which we use for quick tests do not have the capability to handle such requests.


Stay tuned for our next installment of what we learned! Visit our website for more information about our company! www.skeeterbuggins.com! Come and experience the Skeeterbuggins Difference!

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