Tonight I did some stress testing of recording on a separate PC from my main vMix machine. NDI takes up some CPU cycles, but all in all, my main vMix machine ran around 40% CPU (total per Task Manager) vs mid 50%. However, there are notable compression artifacts on the recording. I am thinking this is because I am recording in 1080p (which is what I want to record in), but the settings on my main vMix machine for streaming are set to 720p (this is what I want to stream at). Any way to stream from my main PC at 720p, but have the 2nd PC record at 1080p via NDI and not get the compression artifacts? In other words, can I send a 1080p NDI stream to a networked computer and stream to YouTube at 720p?


Mike

Mike,

What are the specs of the two PC's especially the graphics cards?

I am doing almost exactly what you are talking about. My main PC (i7-2600K with Nvidea 750ti) is set to operate at 1080p in vMix. My 2nd PC (ASUS ROG i7 with Nvidia 970m) is also set to operate at 1080p in vMix. Main PC sends 1080p to 2nd PC via NDI. 2nd PC streams 720p and records 1080p. Main PC does all the production (green screen, videos, graphics, cameras, screen captures, etc.). Main PC runs about 45% CPU. 2nd PC about the same. Sweet setup.

Hope this helps.

- Tom

In vMix, what about setting your Master Output Size to 1080p, keep your External2 at 1080p (configured for NDI out) and have your streaming (External) at 720p (looks like you can enable External2 for NDI as well).

Or, if possible, keep External at 1080p (configured for NDI out), External2 for streaming at 720p.

Okay. I guess I'm blind as I do not see the difference. And how should an artifact in chat be caused by vMix? What am I missing?

- Tom

Hi,

To confirm some points made here, the "vMix - Output" NDI source is always using the Output Size set in Settings -> Display
it does not scale down if the Recording, External are at smaller resolutions (such as for streaming) so it will always be at the highest quality possible.

It's hard to tell what is causing which artefacts in the screenshots provided, as these have been through many layers of processing, including to JPEG
for uploading here!

A more scientific test would be to do as follows:

1. Add in the desktop at full screen of the web page into PC1 from PC3 using NDI. Make sure no scaling, zooming or cropping is being used.
2. Create a snapshot of the output in PC1 using the snapshot (camera) icon in bottom right hand corner of vMix. Save as PNG.
3. On PC2 add in the "vMix - Output" from PC1 and take a second snapshot. Save as PNG.

Upload both PNG files for comparison.

The first should have a small amount of compression as is added by NDI.
The second should be more or less the same as the first, as NDI in theory should not introduce more artefacts over multiple generations.

If there is a big difference I can submit a bug report to NewTek for investigation.

Some final points on NDI:

* NDI does add some compression, similar in many ways to JPEG.
* If you zoom into a NDI source from the receiver, this may become more noticeable. In general NDI sources should be kept at full resolution
and apply zooming at the source instead (such as zooming the text in the web browser and making the window bigger)

Regards,

Martin
vMix

Awesome!! Thanks so much Martin. I take it you don't need me to perform the test mentioned above any more. If so, let me know and I will glad to do it.

Thanks Martin!