Yes, the Nvidia or the AMD GPU on the PC and the GPU of the Quest2 both have accelerated instruction sets to do the encode and decode required - the H.264 ( or other choices )compression algorithm usually provides about a 10 (and as high as 50) to 1 reduction or more on the amount of data for a given image. If you get the performance display enabled on the Virtual Desktop application, you can get an idea of how many milliseconds the PC GPU takes to do the compression encode, then how long it takes to get that over WiFi to the Quest2, and finally an estimate of how long it takes for the decode by the GPU of the Quest. The last two elements only add to the latency between the PC and the Quest2 whereas the encode which takes several milliseconds does add to the frametime and reduces the FPS. If you do the math on the Quest2 resolution for the final transfer to the Quest2:
1832x1920=3.5Megapixels or 28 megabits, then divide by 1Gbps for the approximate speed of the wireless connection in bits-per-second, then divide by 10:1 for the compression, you get about 3 milliseconds for the actual frame transfer. Add the decode time of several milliseconds on the Quest2 and you get the added latency. The math for the Link should be nearly the same since it is a serial transfer as well and the Oculus app test of the Link usually reports about 2 Gbps which is somewhat (maybe double) faster than wireless. The difference in the image quality should only have to do with the parameters of the encode-decode sequence.
But, but…
I another recent post about the usb cable for link, I did a measurement of the real traffic on my usb cable whilst I was in flight , 2000 feets, in the TBM, very smooth even by turning head left and right, and the used bandwidth was 88 Mbps at max… On a cable tested at 1.7 Gbps !!!
So we never use that bandwidth at all with usb link…
Virtual Desktop has a setting (withing the VR app, not in the Windows streamer app) that allows it to change your desktop resolution to the optimal resolution for VR depending on your headset. It probably switches your monitor to an unsupported resolution setting. When you switch it off things will probably return to normal, or maybe it won’t trigger this problem again after restarting your computer.
Thank you for the good explanation. I have one more question: is it possible that Virtual Desktop was programmed in such a way that its stream encoding and decoding are more efficient than those behind Oculus Link? If so, for low end PCs like mine, using VD may see better performance than using Oculus Link, while better PCs won’t see much difference.
I am in the process of evaluating that…
With Link cable , I get audio dropouts, which MAY be indicative of DATA Drop out . With Virtual Desk Top,I have not seen this problem, but…
- I cannot use Virtual Desktop unless I change my OpenVR Runtime to look at SteamVR openXR. My FPS counter via Developer mode cannot be viewed, thus FPS cannot be evaluated… It is offset to the upper right and unviewable even by rolling eye to view. Am I the only one?..the only alternative is FPSVR via Steam, but that may cause some effect on FPS itself, since Link cable does not use SteamVR.
regards,
Chas
I use FPSVR just when needed to figure out the fps impact of my settings, then disable it when I’m set since it causes stutters for some reason.
Yes, I tried Link again last week for a few hours and definitely always get better performance with VD. Also sometimes have glitches with Link while VD is always clean.
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