your symptoms suggest a system issue [security setting?]
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a blank video suggest that maybe some of the required files are not in same location?
are you putting the produced files in a sub folder [a setting in the production wizard?
what type of production are you doing?
What I am basically doing is creating a powerpoint presentation then I run through the powerpoint presentation and record the screen while the presentation is running (i use a text to speech engine to record audio narration in the presentation), save the recorded presentation to MP4 video, import the Mp4 to my timeline in camtasia studio add my callouts and animations as required, and then output the final product from there to HD Video. Perhaps its overkill or conflicting my browser to produce using HD 1920x1200 resolution but I want these productions to be HD quality.
Are you uploading your video and it can't play?
Have you tried to just drag and drop the html file directly in to a browser on you desktop and see if it plays?
If so than I would suspect something in the coding of the .html, If you can not play the .mp4 in the browser
Than I would suspect an issue with your browser settings or maybe an add-on issue.
I would be glad to check from my end if you have link or want to send me a test production
I've run into this issue as well while producing eLearning courses through Lectora. This happens no matter whether I produce using the standard MP4 output or the Lectora output (both without the controller).
I have an example up online and if you Inspect Element, the console shows that there is an error decoding the file. I did some research and this was actually something that happened with Firefox several versions ago (the 30.x versions if I remember right).
Doing some work with another developer, he was able to take the file, re-encode with a different encoder and it would work. That said, this is one that could fall on Camtasia's or Firefox's shoulders.