The title already explains my problem. I can manually change the src="…" of a video element in the Firefox Inspector, by double clicking on the src="…" and editing it. The player shows the video (actually the same video, just a higher resolution) and I can start it.
When I try to do this programmatically it fails: “The media could not be loaded, either because the server or network failed or because the format is not supported”.
var video = document.getElementById(“video_html5_api”);
var str = video.src.replace(“720p.mp4”, “1080.mp4”);
video.src = str;
Any idea how I can fix this problem? What is the manual way doing differently?