Some interesting test results performed today using different types of video capture connections - USB, PCIe, Thunderbolt and NDI. The devices included:
1) Magewell Pro Capture Quad HDMI card mounted in an external Zotac AMP Box Mini Thunderbolt 3 PCIe enclosure.
2) Magewell Pro Capture All-In-One card installed internally in a PCIe slot on the Asus Z170 motherboard.
3) Magewell Pro Connect 4K NDI converter.
4) Magewell USB Capture HDMI Plus via a USB3 port.
The signal source was a Blackmagic Mini Monitor 4K card, connected via a 4-way HDMI DA to the capture devices, and outputting a 1080p60 test signal with in-vision frame numbers and fairly complex video content - in order to give the NDI converter some work to do! You can see that the Pro Convert dashboard shows an outgoing data rate of 185Mb/s.
ProConvertDashboard1080p60.PNG
(76kb) downloaded 7 time(s). The vMix test setup was simply those four camera inputs, a text overlay and an image multiview showing a quad split overlay of the four main sources.
QuadTest1-4Oct18.PNG
(750kb) downloaded 30 time(s). What you see is that the NDI converter holds its own against the two PCIe capture cards, with the USB device appearing to be one frame behind. However, in the snapshot frame grabs produced by vMix, all four sources are typically in sync, all showing the same frame.
Sample "image output snapshot" file
vMix Capture 04 October 2018 10-50-39.png
(3,794kb) downloaded 10 time(s).Changing the order of the inputs did make a slight difference. By putting the NDI & USB devices as the first two inputs, with the PCIe devices as 3 & 4, all four devices were showing in sync, both in the GUI preview and in the output snapshots. So it may be worth arranging your inputs with what you think may be slower devices as the lower numbered inputs. However, in these tests it was really only the USB device that appeared slightly slower than the PCIe cards, with the NDI converter providing similar overall latency to the PCIe cards.
QuadTest2-4Oct18.PNG
(748kb) downloaded 31 time(s).Sample "image output snapshot" file from the revised input order
vMix Capture 04 October 2018 10-35-57.png
(3,970kb) downloaded 9 time(s).