I've been struggling with showing mp4 files on web pages.
When dropping files into Xara it very often refuses to accept the format. Sometimes it does, and sometimes it doesn't.
Exactly what are the requirements? AVC and Sony are key words here?
I have usually got good/working mp4 files using http://www.apowersoft.com/free-online-video-converter
When using WinX converter I get mp4 files hat will not work.
Running working mp4 files through mp4-faststart seems to not always work that well?

When dropping files Xara unfortunately always writes code for showing with Flash. Only if the page is shown on Android, iOS etc will it use the HMTL5 standard <video> tag. A PC browser without Flash installed/enabled will not show anything :-(
The Flash player used will not show any picture before starting to play :-(

After fiddling around I found out that I have to do this manually to get the results I want, so I either edit the tag used to:

Code:
<script type="text/javascript">
document.write("\x3cvideo src=\"index_htm_files/Plak7f.mp4\" controls width=\"100%\" height=\"100%\"/>");
</script>
or:
Code:
<video width="100%" height="100%" controls>
  <source src="index_htm_files/Plak7f.mp4" type="video/mp4">
  Your browser does not support the video tag.
</video>
Both works fine in a browser offline or online, both on Windows10 (Opera, Firefox, Chrome, Edge and IE) and Android (Opera), but both usually also fail in the preview inside Xara :-(
In the browser they also show the first frame of the video before playing, which is much better than showing nothing..

Time for an overhaul of the video "widget" in Xara? And the Preview engine options (adding Edge?)?