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NDI Screen capture stuttering and Low FPS
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Joined: 10/21/2020(UTC) Posts: 17  Location: Bulkington Thanks: 5 times
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I know there are a few posts like this, but I didn’t want to hijack their posts with my problems! 😬
I’m getting low frame rate on NDI capture (or NDI Scan converter), from my playback laptops. I know the FPS dynamically changes depending on the content, but I regularly see frame drops and stuttering within vMix (and NDI monitor!).
The laptop specs are decent enough, Dell XPS 15 with GTX1060 cards and i7 or i9’s. I’m also running on a 10Gb switch, although my laptops cards are only 1Gb.
vMix NDI feeds are fine and smooth.
Have tried hardware acceleration on and off same results. CPU and GPU are both running at low % generally NDI seems to have little impact.
I’m thinking I may need some hardware encoders, but if I can avoid the outlay I will.
Any help is appreciated! 👍
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Joined: 7/1/2015(UTC) Posts: 1,151   Location: Houston TX Thanks: 319 times
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High-frame-rate capture requires a hardware solution.
I use a Birddog Mini connected to the HDMI output of my laptop. It gets me 60 fps reliably.
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Joined: 5/13/2014(UTC) Posts: 518 Location: Manchester, UK Thanks: 2 times
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If you end up going down the hardware encoding route for laptop output you might also want to consider the Magewell units as well as the BirdDog units, if only because the Magewell units can accept a wide range of GPU resolutions and aspect ratios, not just the 720 & 1080 broadcast resolutions which the BirdDog accepts, and that can be handy if you're ever faced with a computer or split-projector feed that defaults to something like 1366x768 or 1600x900, or even an old non-16:9 aspect ratio like 1280x1024 or 1600x1200.
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 1 user thanked zenvideo for this useful post.
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Quote:I know the FPS dynamically changes depending on the content ??? FPS and bitrate are 2 different things Quote:I regularly see frame drops and stuttering within vMix (and NDI monitor!). What is the framerate frequency of your monitors on the captured devices? If 100Hz or above, try reducing it to "standard" 60Hz.
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Joined: 10/21/2020(UTC) Posts: 17 Location: Bulkington Thanks: 5 times
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The FPS is dropping to 15, when playing a full motion video, it looks like it’s stuttering, because it has such a low frame rate.
I don’t know how to monitor the bitrate of an NDI signal, but the FPS is shown on vMix NDI capture, which is where I am referencing the problem.
The frame rate I’m trying for is 25 or 50 which should be fairly simple.
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Originally Posted by: mcook75 
The frame rate I’m trying for is 25 or 50 which should be fairly simple.
Nope. Not simple at all. Your video card is designed to present the stream to a display. It's doing that successfully. Then you ask it to do a simultaneous, equally difficult task. Capture what it's displaying, sending it to the CPU for encoding into NDI. Only VERY capable GPUs can do this. OTOH, mirror the display to a second output and capture that a card in a separate PC or an NDI encoder like my BirdDog Mini or a Magewell NDI interface. You'll get dead reliable results because it's no additional work for the first GPU. That GPU is designed to mirror its output with zero extra effort. The NDI encoder does the heavy lifting.
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Joined: 10/21/2020(UTC) Posts: 17 Location: Bulkington Thanks: 5 times
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Hardware encoding is where I’m going, I’m buys a load today!
The reason I’m chasing my tail, is because both the GPU and CPU show no strain. I’d feel more confident that it was due to a low spec laptop, if the CPU Or GPU were clock above even 50%, it just feels like the laptop’s resources are not being used and something else is causing the problem.
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Originally Posted by: mcook75 Hardware encoding is where I’m going, I’m buys a load today!
The reason I’m chasing my tail, is because both the GPU and CPU show no strain. I’d feel more confident that it was due to a low spec laptop, if the CPU Or GPU were clock above even 50%, it just feels like the laptop’s resources are not being used and something else is causing the problem. All it takes is one bottleneck to fundamentally limit what you can achieve. Is the GPU using memory shared with the CPU? That's one possible bottleneck. I'm working on a blog post that compares using (1) vMix Desktop Capture (2) Newtek Scan Convertor and (3) a BirdDog Mini to see which can reliable capture 1080p60. I predict only the BirdDog device will even come close.
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