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SRT - Dropped packets
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ispyisail  
#1 Posted : Sunday, January 15, 2023 2:19:07 PM(UTC)
ispyisail

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Hi all

Question

Are dropped SRT packets re-sent or just dropped like UDP?

What percentage of dropped packets would be considered acceptable for good quality video transfer?


Using starlink and I would guess some dropped packets are part of a wireless connection

Thanks
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BARP  
#2 Posted : Monday, January 16, 2023 1:50:05 PM(UTC)
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They are re-sent. This is why the second configuration option for an SRT source is latency. You are supposed to set the latency to 3x your average round-trip time in milliseconds. That will normally give enough time for any missed, or out-of-order packets to arrive and keep a smooth stream.
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ispyisail  
#3 Posted : Saturday, January 21, 2023 5:20:46 AM(UTC)
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Originally Posted by: BARP Go to Quoted Post
They are re-sent. This is why the second configuration option for an SRT source is latency. You are supposed to set the latency to 3x your average round-trip time in milliseconds. That will normally give enough time for any missed, or out-of-order packets to arrive and keep a smooth stream.


Thanks for this information
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ispyisail  
#4 Posted : Saturday, January 21, 2023 5:26:44 AM(UTC)
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From the vmix online manual

Quote:
Secure Reliable Transport is an open source video transport protocol. It optimises streaming performance across unpredictable networks, such as the Internet, by dynamically adapting to the real-time network conditions.


Quote:
Latency
Specify the latency of the connection in milliseconds to adapt to network congestion.
The higher this value, the better SRT can handle difficult network conditions.
As a general rule this should be set to at least 4x the ping time destination IP. So 20ms would require a latency setting of at least 80
This must be set to the same value on both ends.



So the question is:

How can we tell if the internet connection is not good enough for a stable video transfer via SRT?

I was using dropped packets as an indication of a good connection. It appears that dropped packets are ok to a point. But where is that point?
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BARP  
#5 Posted : Saturday, January 21, 2023 6:04:14 AM(UTC)
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In my opinion that's a bit of a trick question. In this day and age, if you are getting more than 2% packet loss from your ISP, you should get a new ISP. Even Starlink peaks around 1.2% loss on its worst days. That being said, I have been in situations where all we had was cellular hotspots with nearly 30% packet loss (about an hour outside the nearest city) and turning up the latency to 5,000ms (5 seconds) was enough to get a stable stream.
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ispyisail  
#6 Posted : Saturday, January 28, 2023 4:45:57 AM(UTC)
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Originally Posted by: BARP Go to Quoted Post
In my opinion that's a bit of a trick question. In this day and age, if you are getting more than 2% packet loss from your ISP, you should get a new ISP. Even Starlink peaks around 1.2% loss on its worst days. That being said, I have been in situations where all we had was cellular hotspots with nearly 30% packet loss (about an hour outside the nearest city) and turning up the latency to 5,000ms (5 seconds) was enough to get a stable stream.


Thank you for this insight
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