But sometimes you also need to try to educate the client as to why what they are asking for may be a bad idea. As the developer you have - or should have - a greater understanding of the issues involved than your client is likely to have, and therefore you also have a responsibility to them to explain where they have made a poor choice. Yes, at the end of the day they may still dig their heels in and insist, but at least the responsibility for a poor decision then rests very firmly with them.
Moving images can cause problems for some visitors (and I don’t just mean images which can cause seizures), so there should always be a clear method to stop the video.
Animation should almost always be user controlled or very short in duration. Images that continually animate can cause the rest of the page to be more difficult, or for users with very high levels of distractibility, totally inaccessible.
WCAG 2.0 Success Criterion 2.2.2 (Level A) requires that automatically moving, blinking, or scrolling content that lasts longer than 5 seconds can be paused, stopped, or hidden by the user.
See http://webaim.org/techniques/images/
But what about other users who might, under normal circumstances, be quite happy to view the video, but who happen to access your page in a library, the office, a hospital or anywhere where a sudden soundtrack played without warning could cause issues.
This article is about the problems of auto-play music tracks, but the lessons can be applied to any soundtrack.