Delayed panadaptor video when running RealVNC

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  • Updated 5 years ago
Two of us are running 6700s with SSDR 1.3.8 on Win 7 Pro 64 bit i7 computers and are experiencing delayed panadaptor video when operating remote via RealVNC. It's funny, if I move the slice, it responds as it should and then a few seconds later the signal catches up. Audio is not delayed making things cumbersome with the sound and video so horribly out of sync.

Anyone else seen this behavior?
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W1IMD

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Posted 5 years ago

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Stu Phillips - K6TU, Elmer

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Depending on whether you have a mirror screen driver under RealVNC, I'm not surprised at all and the "fault" lines entirely with RealVNC.

Bear in mind that if you have SmartSDR with default configuration, its rendering something like 24 to 30 frames a second.  RealVNC has to pixel scrape the display, transfer the data as pixel blts to the remote machine and then render it.

In a local network environment with UltraVNC and a mirror screen driver, I see something like 50 MBps going between the two machines.  This in 1 GBps Ethernet.

If you are on a thin network, have sub-optimal compression between the VNC server and client, this is what you are going to experience.  

It is NOT a fault of SmartSDR.

A suggestion or two:

1. Reduce the frame rate in SmartSDR - you may have to go down to 2-3 per second depending on the bandwidth available.
2. If practical use a mirror screen driver - I don't know if RealVNC supports one but UltraVNC does 0 however, be aware that it then causes SmartSDR to be unable to use full GPU acceleration.
3. Reduce the size of the window for SmartSDR to reduce the number of pixels that have to be updated.
4. Make sure you have enough bandwidth between the two machines.

With a heavy graphics application like a hi-res game or SmartSDR, you need to be really aware of the amount of screen updates that are being made...  30 frames per second at 1024 x 1024 pixels with three bytes per pixel color... well, thats a heck of a lot of data.

Stu K6TU
(Edited)
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W1IMD

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Thanks Stu. Perhaps I can load an older version of RealVNC and try again as this behavior is pretty new. I've been using my station remotely for years and never saw this before.
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Larry da Ponte

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I've experienced out of sync pan video and audio directly connected to the radio but it only happens occasionally.
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W1IMD

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Stu, you have done it again. I have lowered the frame rate to 10 FPS and the delay has become much, much shorter and we can live with that.

A great mind and a contester too. Whodathunkit?

Merry Christmas to you and yours.
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Ric Plummer

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I have been running this for a while. Remote is on FiOS so 30/25 Mbps, But the radio is on cable with 20/2 Mbps and the radio only being able to upload the screen at 2 is a definite limit. Thanks Stu for the info, I didn't know I had the update rate available to change. Merry Xmas to all Flexers. Ric KV1W