Align textField with boundaries of a video

Hello everyone, I need help for that little matter in AS3. I’ve create a textField like that:

import flash.text.TextFieldAutoSize;
import flash.text.TextField;
private var _playbackTime:TextField;
_playbackTime = new TextField();
_playbackTime.autoSize = TextFieldAutoSize.LEFT;
_playbackTime.textColor=0xE60000;
_playbackTime.y =20;
_playbackTime.x =20;
_playbackTime.text = “RECHERCHE DU CANAL”;
And now, the problem is that I want that _playbackTime.y and.x to be align bottom right with an imported flv (as the textField) and add a margin. I don’t want to use predefined pixels because I use variable video dimension. I want to create a tv channel with a logo at bottomright. Can someone may help me with that?