A GStreamer plugin or one of its features needed for playback is missing.
The description and installer_detail can be used to present the user more info about what is missing and prompt
him to install it with an external installer.
| name |
a localised string describing the missing feature, for use in error dialogs and the like. |
| installer_detail |
a string containing all the details about the missing element to be passed to an external installer called via either install_plugins_async or install_plugins_sync function. |