SMPlayer is a media player (front-end for MPlayer) capable of playing almost any audio/video formats such as avi, mp4, mp3, mpeg, etc. The player has many interesting features like the ability to remember settings done to played media files. When closing, for example, a video and re-open it, it will be resumed from the point you ended your viewing of the video with the same settings set (volume, subtitles, etc.).
You can review all features for SMPlayer here. The latest version of SMPlayer is 0.8.1 which brings a fix for Youtube playback problems. To install SMPlayer 0.8.1 on Ubuntu 12.10/12.04/Linux Mint 13 or older, open the terminal and run the following commands:
sudo add-apt-repository ppa:rvm/smplayer
sudo apt-get update
sudo apt-get install smplayer smplayer-themes smtube