Does anyone have any evidence or could point me in the direction of a web page that explains why video and audio autoplay is bad practice. I know it is but i'm struggling to find anything to back this up.
This is the best article that I'm aware of on this topic: http://www.punkchip.com/2009/04/autoplay-is-bad-for-all-users/
Video autoplay is not great if you are a screenreader user. Imagine you open up a new page with a video of Aqua's 'Barbie Girl' and you need to listen to the page in order to navigate your way to the controls of the video but can't hear the screenreader because Barbie Girl is blasting out in the background.
Robin Christopherson from AbilityNet gave a demo of this once and it really illustrated how bad autoplay can be for accessibility.
I can give a few points from my own experience why auto-playing videos/sound can be a bad practice and how decide when to auto-play without these points being an issue...
If the user has a slow connection (or busy connection) then the video keeps freezing - no time to cache it prior to playing.
(Can be fixed by auto-playing only when caching is complete.)
If user opens up multiple tabs/windows from search results, then they all start playing together instead of only active tab/window.
(Can be fixed by auto-playing only if tab is in focus.)
If the video isn't expected (e.g. an advert or product demo, not intentional opening of youtube), then sudden playback of sound is very annoying.
(Relevant only to non-requested videos/sounds.)
To summarize things up; if you auto-play only requested, fully cached videos when video is in focus, then it might not be a bad practice.
If you have a couple of hours to invest, this isn't hard to test for yourself. Just find a few "users" (3 at least, 5 would be fine) and ask them to perform some tasks on a website with autoplay (maybe the site you are working on, if that's the case). After the test, ask them for their general impressions. I bet they will mention the music/video autoplay, and not with a positive note.
It's more than four years since this question was asked, and the Punkchip article is even older (but still relevant).
However, Nielsen Norman Group (NNG) recently revisited the topic of video usability with an excellent article which it's worth referencing here to keep the topic up to date.
Here's the relevant part of the article that refers to autoplay:
When users arrive at a webpage, they don’t appreciate being surprised by video or audio content that begins playing without their consent. Video, and the accompanying audio, can confuse or distract users, and can interfere with their consumption of content on the page.
Those users who do not want to watch the video must devote cognitive resources and extra effort to figure out how to turn the audio off or pause the video, rather than focusing on their goals and information needs. Any movement on the page can be a distraction.
< snip ---- example image of rich email message from Boden ---- snip >
The Spotlight on Style section of this email message from Boden included video that automatically played upon opening the message. Automatically playing video can surprise, if not annoy, users.
Users don’t appreciate being surprised by video content that they do not expect. Links leading to video content should indicate the type of content to which they lead. Users assume links lead to pages filled with text and images, not video. Particularly not video that plays automatically.
Users should have control over what content they listen to or watch. When videos play automatically, many users’ first instincts are to either mute or pause the video. Users should easily be able to start, stop or restart a video, as well as mute it or adjust the volume on it, for any video or audio content on the site.