GNOME screencast feature stops after 30s

GNOME has an integrated screencast feature triggered by the keybinding Control+Shift+Alt+R.

By default it stops after 30 seconds.

With Wayland, since 5.8, it seems to be the only way to record the screen.

Friendly journalists have been asking me about this. Other people have written to tails-bugs@ about it.

• Set max-screencast-length=0 by default (!1049 (merged))
• Update https://tails.boum.org/contribute/how/user_experience/recording/
• Don't mention Kazam anymore in https://tails.boum.org/doc/persistent_storage/additional_software/
• Document this feature somewhere in the doc