Many email programs and readers simply don't like embedded media. They'll either display it incorrectly or push it to spam. ISPs in general don't like seeing that sort of code and tend to flag it, as a lot of malware makes it way into email through that sort of thing.
Our Marketing Mavens recommend that you use a high quality screenshot or image in your campaign. And then, link that picture to the video or audio on your Website, or elsewhere on the web. You could also put a text link instead of an image. See image below:
This is a win/win because it keeps your emails 100% compatible AND drives traffic to your Website.