I don't watch a whole lot of YouTube but when I do I find it frustrating how many ads they show. I'll often click on a video and then decide that it's not what I wanted to watch a couple of minutes into it. At that point I've already watched one or two ads. So instead I've been relying on YouTube's hover previews more and more.
There are the little previews that happen when you hover your mouse over a video either on the homepage or on the search result pages. They don't display ads and you can turn on the volume and time jump to different parts of the video. The problem is you've got to keep your mouse hovered over the smaller video the whole time and you also need to turn on the sound each time.
I found myself wishing that I could improve the user experience a bit and just watch the video without the extra hassle so I built a Chrome extension that pins the preview in place. If you install this extension, now a button shows up when you hover over a video that makes the video bigger, removes the need to keep your mouse hovered over it, and turns on the sound.
I really like to use this as a filter so I can watch a few minutes of the video and if the content is good I'll click through and watch the ads. Technically you could watch the entire video ad free doing this but I would recommend supporting the creators you enjoy by watching their ads or contributing directly.
There are a few caveats. The hover preview is YouTube's own lower-quality clip, not the full resolution version of the video. Some previews don't include audio at all (music videos especially). And it isn't guaranteed to keep working for very long since YouTube updates their player regularly. This was built more as a proof of concept to see if it was possible and as a way to play around with building a Chrome extension.
The extension is open source and available for free.