The best way to understand what that means is to watch the video on that page, but in short: imagine the idea of subtitles mashed with the internet. Instead of just text appearing on screen based on time in a video, any web content can appear in the video – including live web streams such as twitter hashtags.
It’s an exciting development – I blogged about version 0.3 of popcorn.js in February of this year, and it was significantly less coherent and less far reaching – it’s come a long way in a mere nine months.
This is really is the next plane beyond subtitles – something that the Chinese subtitle hackers have been laying the groundwork for over the last couple of years. I can’t find the original article (from Time.com I believe), but it revolved around Chinese fansubs of American tv shows, like Lost, that included metadata from Wikipedia. For example someone in the show mentions General Custer, a topic Chinese viewers might not be familiar with, and since the video can be paused as they are largely consumed on laptops, the entire Wikipedia entry can be added to one frame for cultural context. Obviously, Popcorn.js takes this left field practice to the next level entirely.
Mozilla Popcorn is a slightly larger package that includes Popcorn Maker as well – a GUI for Popcorn.js that means you don’t need to be a coder to utilise the software. In fact, now that I’ve had a better look at Popcorn Maker, it’s very reminiscent of AegisSub or something similar – not as feature rich in what it can do to text, but much more so in it’s Twitter, Flickr, Wikipedia, image and website integration.
I’d be interested to know how much integration there is with another of Mozilla’s subtitling projects – the Universal Subtitle project.