How to play webm (using the VP9 codec) in VLC?

VP9 requires VLC 2.2.

sudo add-apt-repository ppa:mc3man/trusty-media

sudo apt-get update

sudo apt-get install vlc vlc-plugin-*

https://forum.videolan.org/viewtopic.php?t=131211

I had this problem in ubuntu 14.04 and it got solved by installing VLC 2.2.

There is no need to install ubuntu-restricted-extras to be able to play WebM with VLC. VLC 2.1.2 supports VP9 by default (see http://www.webmproject.org/vp9/ and http://www.videolan.org/vlc/releases/2.1.2.html). You might try upgrading VLC or installing the latest stable by downloading it from the VLC site directly.

I've had to apt remove vlc-? before I found out that something from that package was playing havoc with HTML5 video ('vp9' codec)/DASH accelerated video rendering/streaming in Firefox.