Onsite AV feed - RTMP server built onto host/recipient machine?

[kcchtech]

Hello,

Can a single machine (e.g. a raspberry pi) be used as both an rtmp server and to output the feed (i.e. via HDMI)??

If you're interested, the background to this question is as follows:

I am tasked with sending an audio / AV feed to a another classroom in the school our church hires.

I've found instructions for building a separate RTMP server, but would rather build it into the host or recipient machine so there is one less wifi link and one less device to set up. Is that possible? The host is a windows laptop hosing our presentation software, audio recording and obs. The recipient is not yet defined, but could end up being a raspberry pi for example. Its job would simply be to output the feed, so I assume this would be the best candidate.

A few limitations:
- a physical cable is not acceptable
- WIFI network access only, not hard wired. WIFI requires browser sign in each week.
- we will have to request for any school network ports to be opened that aren't open already (NDI's 5961 onwards are blocked)
- the feed must be private
- the feed will ideally be low latency as it is partially audible directly from the hall
- the solution should be simple to use week-by-week by volunteer team members
- the solution should be robust so it needs minimal maintenance/support from me

On the plus side, the video feed only needs to be low framerate and could be as low as 540p if needed. The resolution can be fixed too, so no need to create multiple resolutions.

What I've tried / looked at so far:
- I can get a youtube private feed working but its quite faffy.
- NDI is not stable over WIFI, and as far as I am aware it can't be buffered
- Paid for host services are too expensive (our limited use doesn't utilise the value they are priced for)

Suggestions for other approaches are very welcome.

Thanks very much!

 

[Tomasz Góral]

RPi have very slow WiFi (max speed is 72 Mb/s).
You can play on RPi any video date like rtmp or HLS stream.
I think you need some one who prepare solution on site for you.

 

[kcchtech]

Thanks Tomasz, I wasn't aware of the slow wifi on the RPi.

 

[konsolenritter]

Look at this:

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

www.youtube.com

The example is given with an ATEM mini as the source, but that will work with obs as source from the windows laptop too.
A raspberry pi (with passive alu heatsink) as rtmp server, playing locally via its hdmi out. Exactly what you want, ehh? :)

You may use an extern wifi router/accesspoint. But you were warned about issues related to wifi. If you really can't go with an (even temporary drawn) cable between the rooms, then try wifi.

Personally i would prefer resolution still over framerate if the movements in the content keeps low most times (typical classroom situation?). So you could go with 8..14 mbps for 1080p30. The raspbi will screen locally at 1080p60 which should fit.

 

[konsolenritter]

- the feed will ideally be low latency as it is partially audible directly from the hall

Stability (even for wifi environments) and low latency are direct opposed and conflictive aims for your project. With any rtmp server you'll have definitely more latency than using NDI via cable (while low latency was one of the major development goals for NDI especially)! So its your turn to isolate the rooms acoustically or take rooms apart enough. Keep audio volumes as low as possible while high as needed.

- we will have to request for any school network ports to be opened that aren't open already (NDI's 5961 onwards are blocked)

What exactly do you mean with that? Network ports at wall sockets? Or even firewalls in the wifi? You are strictly encouraged to avoid using any foreign wifi network with conditions you can't control. It makes things even more difficult and errorprone. So if you have to go by wifi then its far better to span your own (additional) wifi during these events and leave the existing school network alone (and idle). And you should encourage your listeners in the hall and in the room to keep their mobile wifi connections off during the sessions, so contributing to the stability of the whole project.

 

[kcchtech]

Stability (even for wifi environments) and low latency are direct opposed and conflictive aims for your project.

Indeed. Its an "ideal" requirement so would be one of the first comprimises to make. I'm trying to explore if there are any low latency options. I know there are wifi assistive listening deevices out there with latency in the 50-70ms range, but they are hardware based encoders. And I know YouTube on low latency setting gives anywhere between 2 and 5 seconds. So was hoping for somewhere around 1 second by keeping the signal on the local WLAN.

So its your turn to isolate the rooms acoustically or take rooms apart enough.

Unfortunately doors have to be open for now due to COVID, and the rooms can't move.

its far better to span your own (additional) wifi

I was considering that. The only issue is our own wifi would not have an Internet connection and the host device needs internet. Not sure if I can have the host device running on 2 networks at the same time? Else I could use a separate device. Also the path is not direct line of sight. Its L-shaped, and when we are allowed to close doors there will be more obstruction. Might give it a try though. May need directional antennae.

What exactly do you mean with that? Network ports at wall sockets? Or even firewalls in the wifi?

Firewalls in the wifi. We should be able to get ports opened if needed as long as the school don't consider them to be a sufficient security risk.

Look at this:

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

www.youtube.com

The example is given with an ATEM mini as the source, but that will work with obs as source from the windows laptop too.
A raspberry pi (with passive alu heatsink) as rtmp server, playing locally via its hdmi out. Exactly what you want, ehh? :)

You may use an extern wifi router/accesspoint. But you were warned about issues related to wifi. If you really can't go with an (even temporary drawn) cable between the rooms, then try wifi.

Personally i would prefer resolution still over framerate if the movements in the content keeps low most times (typical classroom situation?). So you could go with 8..14 mbps for 1080p30. The raspbi will screen locally at 1080p60 which should fit.

This looks helpful. Will take a look.

I realise this project is far from ideal. Just trying to explore the options. Thanks for your input konsolenritter.

 

[Tomasz Góral]

Get info about LLHLS (low latency HLS is subsecond latency), this need open ports number 80 (default port www).
on RPI always is WiFi problem (low speed, of course you can add additional usb device with better WiFi class, antenna).
One device is server www with LLHLS protocol other get signal and play.
I do not recommend running the server and playing on one device.