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pba  
#1 Posted : Sunday, April 19, 2020 9:47:27 AM(UTC)
pba

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Hello guys,

I have a question regarding VMIX SRT Output.

First of all, I use "long distance" SRT input feeds day-by-day with a very good result. The latency is always sub-second, between EU and USA, Asia, etc, and the link is real stable - of course you have to setup the link with the correct parameters.

Yesterday I tried to send back a PGM feed and sound to a remote locations. I'm tested this with Larix Player and Haivision Player Pro. The latency was always higher than 1 second - and this was a local network. I played with the output settings, H.264, HEVC, hardware and software encoding, low-profile encoder, etc., without any success. The latency was always more than 1 second. I can't figure out why its occur... is there any tips, idea, how can I eliminate this? With VMIX CALL (webRTC) the latency is less than 10 frame...

Thank you!

ask  
#2 Posted : Sunday, April 19, 2020 9:57:37 AM(UTC)
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SRT is always fixed-latency. You specify the latency at both ends. vMixCall will adjust based on network conditions.

https://www.vmix.com/help23/index.htm?SRT.html
pba  
#3 Posted : Sunday, April 19, 2020 7:37:06 PM(UTC)
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Yes, you are right, the transmission latency is fixed with the SRT protocol. But here I'm talk about the "glass-to-glass" latency.

The SRT transmission from my iPhone/iPad to the VMIX systems is fine, the glass-to-glass latency is sub-second, so I have a really good results.

The other direction is more problematic: SRT transmission from VMIX output to your iPhone or iPad. I don't know why, but the "glass-to-glass" latency is more than 1 second. Probably this is happen because of the VMIX processing and encoding time, or something similar, I don't know. So I would like to find a way, how can I decrease this processing time as little as possible.

I will try to test out some NDI to SRT util, it can be a workaround, but hey, this is not a real solution. The real solution if we can lower the latency with VMIX SRT output. On input side - it works really well. On output side, its working, but with a relative high glass-to-glass latency, and one-on-one interview situation this is too high, and its not acceptable by the clients.

And its not an SRT latency or player side latency/buffer problem, its quite clear.

VMIX Call can be a good alternative for the return feed, but its a closed thing, so you can't implement in your own solution. And using two device for the conection is not a comfortable option.
admin  
#4 Posted : Monday, April 20, 2020 2:30:33 AM(UTC)
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Glass to glass latency from the vMix SRT output to another vMix SRT input is around 300ms for 1080p29.97 assuming a SRT latency setting of only 30ms.

This would indicate the cause of the latency is due to extra buffering in the mobile player.
VLC for example defaults to a 1000ms buffer.

Regards,

Martin
vMix
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pba on 4/20/2020(UTC)
admin  
#5 Posted : Monday, April 20, 2020 2:37:58 AM(UTC)
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Here is a test setup as an example.
Top left is SRT loopback, top right is NDI loopback.

SRT end to end latency is 266ms or 8 frames.

srt-latency.jpg (296kb) downloaded 5 time(s).
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pba on 4/20/2020(UTC)
pba  
#6 Posted : Monday, April 20, 2020 6:22:43 PM(UTC)
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Hello Martin,

thank you for your answer, this is a very good news! It means, something is not okay with the Larix SLDP / Haivision Pro Player apps. I will try to pick up the contact with them!

Thank you!

Peter


hearelee  
#7 Posted : Wednesday, May 13, 2020 4:56:50 AM(UTC)
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Hi Peter,

did you hear anything back?
I'm having a delay of around 3 - 5 seconds and would like to know how to know how to reduce it as much as possible.
Using vmix -> SRT NimbleStreamer -> SLDP player
Even playing the stream locally with the SLDP player, I get over 2 second delay.

cheers
lee
pba  
#8 Posted : Friday, May 15, 2020 9:40:24 AM(UTC)
pba

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Unfortunately the only solution if you develop a player application for this (based on FFMPEG for example). The latency is not a VMIX issue but SLDP player and Nimble Streamer!
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