A fellow Debian developer recommended this on Debian Planet, I haven't
test it myself.

howto/conference.md

@@ -291,6 +291,12 @@ To quote Ben again:
 > mouth—not directly in front—so that you’re not breathing/spitting
 > into it.
 
+# Testing your audio and video
+
+The above allows for good audio tests, but a fuller test (including
+video) is the [freeconference.com test service](https://www.freeconference.com/feature/free-connection-test/), a commercial
+service, but that provides a more thorough test environment.
+
 ## Pager playbook
 
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