The Poodll filter player system is quite different to other players. It relies on templates and variables and extension handlers. The added complexity makes it very flexible, but it also makes it complex.
Its still a simple task to change the player width or height or other setting. In each template is a “defaults” section. Here the variables are given their default settings. The format is property1=value1,property2=value2.
Note that each template will have different variables/settings, though by convention WIDTH and HEIGHT will be available because the Poodll players do their best to the support the older Moodle size setting system. In that it is possible to set the size of a video/audio player by appending to the media url ?d=[width]x[height] , eg http://nnn.com/blahblah.mp4?d=400×300 .
However with the move to responsive design, some templates will attempt to adjust their size according to the size of the screen. The Flowplayer First Frame player is one of these.