如此处所述克隆 pitivi 后，我安装了 flatpak 。现在运行命令：
sudo apt install gnome-software-plugin-flatpak
我收到这条消息：
gnome-software-plugin-flatpak is already the newest version (3.28.1-0ubuntu4.18.04.12).
并运行以下命令：
cd pitivi-dev/pitivi && source bin/pitivi-env
我收到这条消息：
You need to install flatpak-builder >= 0.10.0 to be able to use the '/home/snpd/github/pitivi-dev/pitivi/build/flatpak/pitivi-flatpak' script.
You can find some information about how to install it for your distribution at:
* http://flatpak.org/
我不知道这里出了什么问题，感谢任何帮助或建议。谢谢。