Rhythmbox does not play music in 16.04 beta

[Frederik Feichtmeier]

When I start rhythmbox normally outside of the terminal, it just does not play the mp3.
When I open a mp3 file in rhythmbox with the terminal this is happening:

frederik@akira:~$ rhythmbox /home/frederik/Musik/AMOK/01\ Before\ Your\ Very\ Eyes....mp3

(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen
(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen
(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen
(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen
(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen
(rhythmbox:3379): Gtk-WARNING **: Duplicate child name in GtkStack: Zur Wiedergabeliste hinzufügen

Then I return to the rhythmbox window and click the play button and this is happening in the terminal:

(rhythmbox:3379): Rhythmbox-CRITICAL **: impl_play: assertion 'mp->priv->playbin != NULL' failed
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.

So rhythmbox can't play mp3's and can't import my music library due to this error I believe.
Ubuntu 16.04. beta2 and a fresh install

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[rithik g (gkrithi)]

The bug is due to missing mp3 decoder plugins

https://bugs.launchpad.net/ubuntu/+source/rhythmbox/+bug/1672035 comment #6 for details on how to get it working.