<p>We often send emails in HTML for clients (Dont like it but not my choice)</p>

<p>Does anyone have any info or a link on support for the dynscrc attribute or img in email clients?</p>

My solution here would be to have a screenshot (perhaps with a 'click to watch' overlay) of your movie that links to a non-mail page that has a player in it.
Dealing with html email, in my experience, isn't so much about having standards as it is learning to compromise.  Web client and (the increasingly rare) desktop clients have differing behaviors that make website browser compliance seem like preschool by comparison.