SMPlayer is my favorite frontend for MPlayer. There are some other frontends, such as MPlayers own GUI (depreciated), GNOME MPlayer, or KMPlayer. But SMPlayer is the best. You probably use VLC or Totem or something I have never heard, I can say 99% MPlayer is the best. So MPlayer + SMPlayer is the best combination in my opinion.

Weeks ago, I found this Auto zoom Shift+W feature, it fills up the gap of video (and the gap of my life as well). You wont see any blank area if the video doesnt contain blank border. You can use Alt+Arrow keys to pan the zoomed area. There is only a slight problem, the OSD on top-left corner, likely would be cut off. I dont have a resolution for this issue, and I havent tried to ask for one yet.

I usually play a playlist of YouTube videos. Some (indie videos) have introduction part, so I use A-B Section (Repeat) to play only the main part. If a videos sound level is too low or too high, I use Equalizer to adjust.

For what I have done to a video, the changes (not including panning) are memorized by SMPlayer. Thats the most awesome feature, it will always play a video (or audio) in a way you want.

Two things I want to add: 1) Because of SMPlayer, I know there is a hack to boost performance in MPlayer, -vo gl:yuv=2:force-pbo:ati-hack (For ATI cards only). 2) Dont forget to turn off Repeat mode (not the one in Playlist window), it means single track repeat mode when you play a playlist.