I bought myself a LinkPi Enc1-v3P model and trying to check its capabilities. I hooked up a FireTV stick 4K to its hdmi input and played a 4K plex stream. The interface on the dashboard shows '1080P60', while i was expecting it to show 4K.
Can LinkPi take in a 4K input?
It can if you set it up that way in the video settings for the Linkpi. Its only 4k30fps however.... my advice, forget about 4k and run it at 1080p 60fps. I have the 5 port and if i set more than a couple to 4k the cpu starts choking... not really relevant for you since you have the single port but i would rather have 60fps than 30. FWIW
100% everything @slampman said... 
if this is the one you have... LinkPi Enc1-v3P
All the LinkPis max out at 4K30 (if they are the ones that support 4K) so make sure you are setting your output from the firetv to that. If I tried to set it to something higher my Apple TV would change the output BACK to the 1080 setting since 4K60 is not supported.
I am running the 5 port version. I don't have the Internet speed to really test it...I drop frames even at 1 input set to 4k youtube stream... AND the encoder specs says max 3 - 4K30 encodes... I am not surprised if it bogs down at 2 though as @slampman says.
Here is a pic showing the HDMI-3 on mine set to 4k30 but I never run more than 1080-60 normally. Just as a side note don't forget these only encode output to stereo also.
Late Edit...
AS I look at the Note on the Amazon listing in this pic...
I see that they say your unit supports 1080P30x4 encoding/decoding..which they say is a reference for what can be encoded/decoded at once.
Which means your unit should support up to 2 - 1080P60 streams (1080P30x2 for each one) OR 1 - 4KP30 stream.
This would also make sense what @slampman said about our units struggling with more than 2 4K30 streams since our spec says 1080P30x8 EVEN THOUGH it also says it can encode 4KP30x3 right above/next to that on their website. 
I am looking to do a 2 tuner ADBTuner setup. Will connect 2 onn 4Kpro to appropriate LinkPi encoders. My question is am I better off with 2 LinkPi Minis or an ENC1-V3 with a USB 2.0 Capture card as mentioned elsewhere? Will the USB solution have lower quality on that port? (it is a bit lower cost than the Dual Mini approach) TIA for any insight.
I did the enc1 and usb. the only shows i'm using ah4c for are cartoons and news, so I only encode to 720p and can't speak to 1080p although I think others report it works just as well
Buying two of either device will give you nice 1080P input. Traditionally, the USB 2.0 on the ENC1v3 has limited video capture to 720P. However, user over in the ADBTuner thread, @mackid1993 said he is getting good results with a ENC1v3 and a nicer USB to HDMI capture device.
I'm a little leery about using the USB 2.0 port even with that report . The Elgato described says it needs a USB 3.0 port. Regardless, 2 LinkPi minis were cheaper than the ENC1v3 and the Elgato Capture card so I went with that.
I can confirm I'm getting 1080p60 out of it. Those Elgato capture cards can go up to 4K30.
I have to say, I'm still perplexed by this. It's a happy development as I was stuck at a max 1080p50 before. Granted I was not using the Elgato. I'm wondering if the newer ENC1v3 have USB 3.0 now.
EDIT: I guess the only way to know for sure is to order an Elgato and a new LinkPi, test with my existing gear. I will report back.
Very interesting. My original release ENC1v3 has always shown hardware supports Super Speed (3.0), but I could never get USB3 devices to enumerate at 5000. Even in your picture, it looks like the Cam Link is connecting at High Speed, so I assume still USB2. That Elgato must be doing some sort of magic. Impressive.
Maybe try picking up an Elgato Cam Link before picking up a new LinkPi? I believe they're on sale right now. Best Buy even has them for same day pickup.
My thoughts exactly! Thanks for contributing to the community.
If I felt like spending the money I could probably find a cheaper one that would do it. There are several on Amazon that advertise 1080p 60fps output USB 3.0. I just knew the Elgato worked so I went with it after I bought one of them.
Well, looks like you made the right choice. I have many of the MS213x chipset based capture cards. They are cheap, but have all capped out at 1080p50 on the LinkPi.
Shared this deal in the ADBTuner Thread:
So I'm dealing with some stuttering on my Nvidia Shield. I've been troubleshooting this for a while. I'm curious if anyone has any recommended settings that might help with that.
Basically, just in normal playback, I will have the player controls pop up, a handful of frames drop, and then it just kind of goes back to normal.
I'm hoping that there's something on the encoder I can tweak at this point. Just not sure if anyone else has experienced this and possibly has a solution.
It seems like my issue is something with the encoder because when this happens the total cache increases in the player. It almost seems like the encoder is falling behind the stream.
Edit: it's going to take a while to know for sure but I had the HDMI output on and I wonder if that was putting stress on the encoder.
Is it possible the Shield is overheating?
No. Unfortunately, I checked the temps over ADB and they were fine. I actually repasted them and like speed wise they're running great.
The problem is it's two Shields, so it's a 2017 and a 2019, both behaving the same way. I tried an Apple TV and it was fine, but I hated it so I returned it, but considering I can't get the shield to work, either Shield, I'm just going to get another Apple TV, I guess.
If anyone buys the Elgato Cam Link 4K and uses a DirecTV Osprey box, beware. It will start freezing with the LinkPi. You have to manage to get into the settings before it freezes and set the resolution to 1080p60. It defaults to 2160p60. Either the encoder or the Elgato Cam Link seems to choke on this. I just wanted to get this posted somewhere in case someone else has the same problem.
Edit:
After hours of troubleshooting, it turns out that particular Cam Link was defective and I was able to fortunately exchange it at Best Buy. The 4K output on the Osprey boxes actually revealed the bandwidth issue with this unit.
