Converting HTML4 To HTML5 Advice Options

[homeuser]

This seems to be the right forum for this but I apologize if it belongs elsewhere.

For a long time I've been helping a friend with his personal, non-commercial website. Recently a problem has developed. The website has some 50+ html files, almost all of which have Flash video, some also with MP3 audio. All of the video and audio recently stopped working. They're all played in the HTML code using MC Media Player which is installed on the website. It's an orphan player, hence there isn't any support for this problem.

The player has worked for many years. The only reason I suspect for its failing is that it's related to the concerted effort to get rid of Flash video, and therefore none of the browsers (Opera, Firefox and Chrome) will play them or the flash player anymore (even for audio). I have a utility that convert's FLV to MP4, one at a time, so it's not a problem to change those files and address that part of it.

But I need two new players in the HTML code, one for video and one for audio, or one combo player, to replace the combo
MC Media Player. I haven't found one that will work in HTML4. I could use a video player, such as DVDVideoSoft Free HTML5 Video Player And Converter, and then look for an audio player (or just use the AUDIO tag). But these require converting the code to HTML5.

Therein lies the problem. I'm familiar with basic HTML but am NOT by any means an "expert". Converting 50+ files from HTML4 to HTML5 is a daunting and dismaying undertaking.

(I converted one FLV to MP4 on the website and tested it along, with an MP3, using W3Schools sample VIDEO and AUDIO "try its" and they both played, so that confirms that the problem is the player.)

Is there a utility that will read an HTML4 file and flag lines that have tags and attributes that are not HTML5 compliant? That would still leave me with a laborious, tedious and lengthy job to try to figure out their HTML5 equivalents and convert the code. But at least I would not have to read every line one-by-one, examine every tag and attribute, and guess what is not upward compatible to HTML5.

Any and all help - experience, advice, recommendations etc. - will be sincerely and greatly appreciated.
Thank you.