I've got databases that show local media in a Web Viewer in <img> and <video> tags with src attribute referencing local media via the file:///Path/To/File.
example (for local MacOS media)
<img src='file:///Volumes/Path/ToFile.jpg'></img> <video src='file:///Volumes/Path/ToVideoFile.mp4' controls='controls'></video>
The former displays nothing, the latter shows an error.
HTML Code that used to work just fine is no longer working since upgrading from FM15 to FM16
The same code works just fine a browser.