I thought it might be worthwhile to share the details of an issue we had on a production last night. On a slightly more complex 1080p30 project with 8 x SDI inputs (Zoom callers), one x SDI output, 8 x vMixCallers, a number of VTs and outputting ISOs for external recording via NDI, we started to see render times peak at 50-80mS and could hear pops and crackles on PGM audio - which we gather was hearing frames being lost (video was also ever so slightly less smooth).

Thankfully there was a break in the program that a downstream vMix machine was responsible for running so we could look in to what was going wrong on our upstream machine and how we could keep render time well below the 33ms ceiling at 30 fps before frames start to get lost.

Reading https://www.vmix.com/kno...nosing-high-render-times we checked GPU settings and everything obvious, tried dropping our NDI ISOs out, explored the impact of the number of vMixCallers...

The key change we eventually made that resolved the issue was to stop External and take PGM out as NDI instead of SDI. That slashed render times to consistently under 20 mS and more like 10mS.

Could rendering External have such an inpact? We were wondering if rendering an external SDI output is CPU and NDI is GPU? Our inputs were all on a Decklink Quad 2 but the output was on an older singlelane Decklink card. We were also wondering if the output card we were using was to blame and plan to try a much newer Decklink Mini Monitor.

Anyone else seen anything similar?

regards, Scott

Standard NDI encoding on a PC is CPU-based (as used for the vMix NDI outputs).