pitivi fail with gst

(ptv-flatpak) shakaran@otorion:~/Documentos/ProjectsSSD/pitivi-dev/pitivi$ pitivi
Using Pitivi prefix in /home/shakaran/Documentos/ProjectsSSD/pitivi-dev/pitivi-prefix
Running in sandbox: /home/shakaran/Documentos/ProjectsSSD/pitivi-dev/pitivi/bin/pitivi
Gtk-Message: Failed to load module "unity-gtk-module"
ERROR - The following hard dependencies are unmet:
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- gstgtk not found on the system