Question: I have a Windows Media Player-Compononent. I want it to fill the whole form except a line at the bottom for some buttons and Text. So Dock-> Fill minus the part at the bottom but when resized, the part at the bottom should resize to left and right but stay at the bottom and the Windows Media Player-Compononent should resize with the form but keep the distance at the bottom.

Answer: 
Add a panel set its dock to `Bottom`, then add a Media(whatever) component set its dock to `Fill`. You're done.
You don't need any additional Panels or SplitContainers. Problem can be solved with proper docking and anchoring. Place your control on form and resize it so that line at the bottom will stay (you can easily do it by setting dock to top). Then set all [anchors](http://msdn.microsoft.com/en-us/library/system.windows.forms.control.anchor%28v=vs.110%29.aspx) of control [(How to: Anchor Controls on Windows Forms)](http://msdn.microsoft.com/en-us/library/vstudio/8y52cxte%28v=vs.100%29.aspx). That will bound all edges of control to edges of form, and you will have constant height line at the bottom of form.

Result (green is your control):

![enter image description here](https://i.stack.imgur.com/hQQXP.png)
![enter image description here](https://i.stack.imgur.com/boyrM.png)