Poster image not resizing or video not stretching
I am using the JW Player plugin for wordpress and want to display a 1920x1080 video and a poster image (960x540 pixels) on a responsive web page with 960 pixels maximum width.
When I select the player size "Responsive 16:9" and the stretching "stretch proportionally (black borders" in the player management settings with default rendering "html5" then my poster image stretches correctly and fits the frame even when resizing the browser window. The video, however, is much smaller than the frame (maximum width 960 pixels) and therefore has big black borders on all four(!) sides.
When I select the stretching "Keep original dimensions" then my video stretches correctly and fits the frame even when resizing the browser window. The poster image, however, always remains in its original dimension, so when resizing the browser window, the image is cropped on all sides.
What do I have to do so the video AND the poster image will always fit the (responsive) frame?