Computer screen image repeated on mutiple remote monitors, no cable, low latency - Page 1
Forum section: electronics / projects

author: peteb2
author_rank: Regular Contributor
timestamp: February 04, 2018, 10:55:05 pm
content: In the big process we've trialed USB-LAN over Wifi and even 'played' with iPads and apps but there tends to be a huge delay as the source (host) computer display data is "wrangled" to the remote screens.There is no possibility of cable so it has to be some sort of wire-less. The distance is maximum 30metres. Simplex is fine, fundamentally just repeating the screen image produced by the host computer SIMULTANEOUSLY on a group of other screens (HDMI i/p perhaps) with native resolution of 1920x1080.Is there a better approach? I kind of feel we're missing something very fundamental too as i am more a design something, prototype it and then make rather than keep trialing off the shelf 'gadgets'....

author: james_s
author_rank: Super Contributor
timestamp: February 04, 2018, 11:28:46 pm
content: They make off the shelf wireless HDMI links, I've never used one so I don't know how well they perform but that's where I'd start looking.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 05, 2018, 01:54:55 am
content: The LG wireless HDMI modules can be easily hacked to work with any HDMI device and 30m range can be achieved if there's line of sight. No idea how to hack them to send one stream to multiple monitors.https://www.eevblog.com/forum/reviews/teardown-$10-wireless-hdmi-kit/

author: helius
author_rank: Super Contributor
timestamp: February 05, 2018, 02:07:19 am
content: Multicast is fundamentally incompatible with HDCP, so that would have to be disabled. Beyond that, there is no conceptual problem with broadcasting a video signal to multiple receivers.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2018, 07:23:52 am
content: HDCP is trivial to bypass, I have a $20 HDMI splitter from China that strips the HDCP, we actually used them specifically for that purpose at a former job to enable an automated test system to capture HDMI streams.

author: Jeroen3
author_rank: Super Contributor
timestamp: February 05, 2018, 07:41:20 am
content: What's on the screen? You can broadcast the desktop with VLC or OBS (although not yet locally), and play the stream somewhere else.Sync of the screens will be problem, as well has high bandwidth content. But it's something.VNC can also work as one-to-many screen sharing kit.

author: peteb2
author_rank: Regular Contributor
timestamp: February 05, 2018, 09:14:49 am
content: Thanks but the emphasis here is feeding whatever is displayed by the Host PC on its screen out to a group of other screens (that offer the same resolution ability) without the use of any cables (there is no option for them) and to have very, very small latency delay so that any changes occurring on the Host PC also occur on the remote monitors as soon as possible if not in-sync.So far anything i have trialed has an unacceptable latency... That's due to the conversion processes underway for WiFi.I'm beginning to think some kind of short range high-def video transmitter in the wireless mic band (which in my country is the HD channels for terrestrial TV)... 2.4GHz band as shared by WiFi could be a go but again i bet the latency will be just way too much....

author: Someone
author_rank: Super Contributor
timestamp: February 05, 2018, 10:20:27 am
content: Quote from: peteb2 on February 05, 2018, 09:14:49 amGo right for the pro solutions, both of these do multiple receivers from a single transmitter in the 5GHz band (shouting will commence if you now reveal there are multiple heavy walls in the way):http://www.boxx.tv/products/atom-zero-delay-hd-video-assist-system/http://ikancorp.com/productlisting.php?id=193&categoryname=wireless-transmittersI don't know if there is a distributor that carries both so you could compare easily.

author: Jeroen3
author_rank: Super Contributor
timestamp: February 05, 2018, 01:34:51 pm
content: Whatever is on the screen isvery importantin choosing transmission medium.You're asking Full HD, but that does not tell you anything about thebandwidthrequired.If you're showing keynotes, compression techniques will reduce the bandwidth significantly.But if you're streaming FPS action games, then that same bandwidth as a keynote will cost you quality or framerate.You could use a 56k modem for 1920x1080, you'd just have a terrible framerate, or awful artifacts.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2018, 09:15:29 pm
content: The fact that he emphasizes the need for negligible latency suggests that the bandwidth needs to be high enough to transfer a 1080p picture at the full 60fps.I would probably use HDMI splitters of the sort I mentioned coupled to several of those wireless HDMI kits, but I'm sure there are other options. Also HDCP may not be an issue depending on what the signal source is, generally that only matters for protected content like DVD and set-top boxes.

author: peteb2
author_rank: Regular Contributor
timestamp: February 07, 2018, 10:42:06 pm
content: We'd be transmitting a simple PC screen GUI of mainly lines of coloured text that changes from time to time on a slate background. Because the text needs to be readable, maximum quality is a priority. I'll study the suggested 5GHz link kits suggested... thanks.

author: John Heath
author_rank: Frequent Contributor
timestamp: February 08, 2018, 02:28:53 am
content: I was wondering if you are trying to transmit video. This could run into problems. Windows or third party remote computer control software do not transmit video. They only transmit changes to video. Why transmit the same frame over and over again 100 times a second if it is for the most part the same information. It is redundant information that will hog the band width of your network. Possibly the use of remote desktop that comes with windows would be better your application as it will not transmit video. It will only transmit changes to video which requires far less band width?

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 08, 2018, 02:55:28 am
content: Quote from: John Heath on February 08, 2018, 02:28:53 amInter frame compression is basically standard in every modern video codec. And in my experience, most remote desktop solutions are not particularly low latency. The only two I have worked with that are very low latency are Dell iDRAC and Nvidia game streaming, both of which use hardware encoders.

author: John Heath
author_rank: Frequent Contributor
timestamp: February 08, 2018, 06:27:47 am
content: There are time when I need to control someones computer that is 1000 miles away to sort out some issues. When I move my mouse I can see their mouse move without a lot of delay or latency. There are other times when it is difficult to log on and when on it can hang up on you, This means logging on again. From this my guess is the local net is the problem. I can log on to my computer at home with my cell phone it is seldom has a problem. The point I am getting at is more often then not it is the local in house net that you are connecting to that will have a latency problem , in my experience.Leaving this aside when setting up a live video connection in my case it is always a dedicated line that uses the same copper or fiber line as a network but it is not compatible with network protocol. There is no IP address. It is just raw video RGB being punch out in data packages with little room for delays or sudden interruptions. The idea of putting this on a network is unthinkable. On the other hand there is video conferencing that does exactly that using the network as well as remote computer control.Video Codec files is another story. Why does every software I install say my codec files suck and must be replaced with their newer and better codec files. What is wrong with windows standard compression codec files? Why is it not standardized? And why would any programmer worth their spit use the latest codec files knowing it will most likely not be compatible with most older computers without changing all the codec files. Is it just me?

author: Marco
author_rank: Super Contributor
timestamp: February 08, 2018, 07:01:37 am
content: Quote from: peteb2 on February 05, 2018, 09:14:49 amIt's not about conversion, you're just not guaranteed to get any time on the air any time soon when there is congestion.WHDI can supposedly do point to multipoint broadcast, I see sets around for 300$ a piece. Supposedly at low latency, I assume it's a shouty protocol which doesn't even try to play nice with other 5 GHz users.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 08, 2018, 07:49:16 am
content: WHDI is what the LG kit uses. It does try its best to coexist with Wifi, usually using the mid band that is used less. One thing to note is that the LG kit is apparently optimized for gaming since as the signal weakens, it keeps full framerate but the compression artifacts become more visible.