Watch Together with WhatsApp on the side

A virtual party

This weekend, I threw a Virtual Free Fringe party for some friends. The party was under-attended, but it’s fine because I got to experiment with some tech that I’d been meaning to try.

Phootgraph of a wall-mounted television screen. On the screen, comedian Peter Buckley Hill sits with his guitar on his lap in front of an audience: the "PBH's Free Fringe" logo is on the curtain behind him. On the left of the screen a series of WhatsApp messages appear, including one showing a photo of Dan holding a can of Old Speckled Hen beer.
The Abnibbers and I have experimented with watching things together, but apart, before, but this is the first time we’ve watched stand-up comedy this way.

If you ever want to run something like this yourself1, here’s how I did it.

My goals were:

  • A web page at which any attendee could “watch together” a streaming video2,
  • A “chat” overlay, powered by a WhatsApp group3 (the friend group I was inviting were all using WhatsApp anyway, so this was an obvious choice), and
  • To do all the above cheaply or for free.
Selfie photograph of Dan, in a bar with a rooftop view of daylight out the windows in the background, looks concerned as he stares at the a frothy, bubbling flask of yellow liquid he's holding.
I’m a big fan of experiments. Contrary to this picture, though, they’re usually software experiments.

There were two parts to this project:

  1. Setting up a streaming server that everybody can connect to, and
  2. Decorating the stream with a WhatsApp channel

Setting up a streaming server

Linode offers a free trial of $100 of hosting credit over 60 days and has a ready-to-go recipe for installing Owncast, an open-source streaming server I’ve used before, so I used their recipe, opting for a 4GB dedicated server in their London datacentre: at $36/mo, there’d be no risk of running out of my free trial credit even if I failed to shut down and delete the virtual machine in good time. If you prefer the command-line, here’s the API call for that:

curl -H "Content-Type: application/json" \
-H "Authorization: Bearer $TOKEN" \
-X POST -d '{
    "authorized_users": [
    "backups_enabled": false,
    "booted": true,
    "image": "linode/debian10",
    "label": "owncast-eu-west",
    "private_ip": false,
    "region": "eu-west",
    "root_pass": "[YOUR ROOT PASSWORD]",
    "stackscript_data": {
        "server_hostname": "[YOUR DOMAIN NAME]",
        "email_address": "[YOUR EMAIL ADDRESS]"
    "stackscript_id": 804172,
    "tags": [],
    "type": "g6-dedicated-2"

The IP address got assigned before the machine finished booting, so I had time to copy that into my DNS configuration so the domain was already pointing to the machine before it was fully running. This enabled it to get its SSL certificate set up rightaway (if not, I’d have had to finish waiting for the DNS change to propogate and then reboot it).

Out of the box, Owncast is insecure-by-default, so I wanted to jump in and change some passwords. For some reason you’re initially only able to correct this over unencrypted HTTP! I opted to take the risk on this server (which would only be alive for a few hours) and just configure it with this limitation, logging in at http://mydomain:8080/admin with the default username and password (admin / abc123), changing the credentials to something more-secure. I also tweaked the configuration in general: setting the service name, URL, disabling chat features, and so on, and generating a new stream key to replace the default one.

Now I was ready to configure OBS Studio to stream video to my new Owncast server, which would distribute it to anybody who tuned-in.

Screenshot showing OBS Studio window with Start Streaming enabled. The layers "VLC", "Abnib Logo", "WhatsApp icon", WhatsApp prompt", and "WhatsApp" are visible. Elsewhere on the screen, a WhatsApp Web view is visible, with its CSS tweaked to give it a red background, among other changes.
Next up, we need to make WhatsApp appear on the stream with a little bit of CSS hackery.

Decorating the stream

I configured OBS Studio with a “Custom…” stream service with server rtmp://mydomain:1935/live and the stream key I chose when configuring Owncast and kicked off a test stream to ensure that I could access it via https://mydomain. I added a VLC source4 to OBS and fed it a playlist of videos, and added some branding.

With that all working, I now needed a way to display the WhatsApp chat superimposed over the video.For this, I added a Window Capture source and pointed it at a Firefox window that was showing a WhatsApp Web view of the relevant channel. I added a Crop/Pad filter to trim off the unnecessary chrome.

OBS Studio screenshot showing a WhatsApp Web (Window) source tied to a Firefox window and with Crop/Pad and Chroma Key filters applied.
The same technique, of course, could be used to superimpose any web page or whatever other content you like onto a stream.

Next, I used the Firefox debugger “Style Editor” to inject some extra CSS into WhatsApp Web. The class names vary frequently, so there’s no point we re-documenting all of them here, but the essence of the changes were:

  1. Changing the chat background to a solid bright color (I used red) that can then be removed/made transparent using OBS’s Chroma Key filter. Because you have a good solid color you can turn the Similarity and Smoothness way down.
  2. Making all messages appear the same (rather than making my messages appear different from everybody else’s). To do this, I added:
    • .message-in, .message-out { align-items: flex-start !important; } to align them all to the left
    • [aria-label="You:"]::after { content: "Dan Q"; height: 15px !important; display: block; color: #00f !important; padding: 8px 0 0 8px; } to force my name to appear even on my own messages
    • [aria-label^="Open chat details for "] { display: none; } to remove people’s avatars
    • [data-testid="msg-meta"] { display: none !important; } to remove message metadata
    • A hacky bit of CSS to make the backgrounds all white and to remove the speech bubble “tails”
  3. Removing all the sending/received/read etc. icons with [data-icon] { display: none; }

I aimed where possible to exploit selectors that probably won’t change frequently, like [aria-label]s; this improves the chance that I can use the same code next time. I also manually removed “old” messages from the channel that didn’t need to be displayed on the big screen. I wasn’t able to consistently remove “X new messages” notifications, but I’ll probably try again another time, perhaps with the help of an injected userscript.

A little bit of a shame that more people didn’t get to see the results of this experiment, but I’m sure I’ll use the techniques I’ve learned on another ocassion.


1 Or, let’s be honest, if you’re Future Dan and you’re trying to remember how you did it in last time.

2 We were to watch a show by one of my favourite comedians Peter Buckley Hill, the man behind the Free Fringe. I’ve written about him previously… here, there, also several times in 2012 when I also helped make an official digital map of Free Fringe venues. I was especially delighted to have my photo taken with him in 2006. I might be a bit of a fanboy.

3 This could probably be adapted for any other chat system that has a web interface, so if you prefer Telegram or Slack or whatever ever, that’s fine.

4 OBS’s VLC source is just amazing: not only can you give it files, but you can give it URLs, meaning that you can set up a playlist of YouTube videos, or RTSP security camera feeds, or pretty much anything else you feel like (and have the codecs for).

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