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NDI inputs dropping frames / stuttering
Rank: Newbie
Groups: Registered
Joined: 10/9/2020(UTC) Posts: 2 
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I have been having consistent problems with NDI inputs dropping frames/stuttering in vMix, I am seeing this visually in vMix and also by looking at the performance statistics in vMix (dropping over a 1000 frames a minute per source).
I am running the NDI Scan Converter tool on all our Windows PC + Mac to capture the screen (Mostly PowerPoint and Videos) and I am having the same problem on all of the computers (I have also tried running the vMix Desktop Capture on these different computers and same problems again).
I have a gigabit network switch and have done Speedtest on all of the computers and getting around 700mbps each time, I have tried using another network switch (also tried WiFi and same problem again), tried different network cables but still getting the same problem. I have tried running vMix on 2 different desktop computers + Surface Pro and still same problems. I have made sure I am running the latest version of vMix on all of the computers, latest Windows update and latest graphic drivers. FYI the computer I am currently using for vMix is a brand new PC which is 1 week old and still having the same problems.
One interesting thing I have noticed that doesn't get this problem is if I output the vMix PGM (via vMix not Scan Converter) from our second vMix computer with NDI and I put the input into my new vMix computer I don't get any frame rate drops or stuttering, runs perfectly smooth (I have even checked this running vMix on my Surface and I get smooth results again).
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Rank: Advanced Member
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Joined: 4/23/2017(UTC) Posts: 1,210  Location: Germany Thanks: 3 times
Was thanked: 168 time(s) in 150 post(s)
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It seems you have done a lot at both ends. You should check the middle as well. Network, switches, Routers, etc... NDI puts a lot of load on the network. The rule of thunb is that 4 or 5 NDI feeds are doable over a 1G network.
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Rank: Member
Groups: Registered
Joined: 6/4/2020(UTC)
Posts: 15
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I've been trying to diagnose some NDI dropped frame issues here as well using Scan Converter or vMix Desktop Capture. Is it possible that the Source Dropped frame count increasing in vMix might be caused by Scan Converter (or VDC) not sending new frames when nothing changes on the screen? I've noticed considerably lower dropped frame counts when video is playing compared to a static image for example. If so perhaps the rising number of dropped frames isn't necessarily something to worry about?
That said, I'm still experiencing some stutter and general playback inconsistency testing NDI on EC2 g4dn instances which are more problematic as they're noticeable on playback within vMix.
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Rank: Newbie
Groups: Registered
Joined: 10/9/2020(UTC) Posts: 2
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I have a feeling it is, I contacted vMix Support and they were saying dropped frames is normal for NDI Scan Converter as just what you said they don't send new frames when nothing changes on screen. From what I understand, NDI Scan Converter isn't the best tool to use for capturing video playback but instead for graphics like PowerPoint, Desktop Capture and basic animations.
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