BBC iPlayer Goes H.264
The BBC iPlayer team works hard to release new versions of the BBC iPlayer frequently in its bid to make it as widely available as possible across different devices and to come up with the most exciting new features.
Though not as sexy, the team also has to address the [inevitable] bug fixes. Over the past six months we added Flash streaming (Dec), added Most Popular, More Like This, etc. (Jan), and made BBC iPlayer available on iPhone (Feb) and Wii (April).
We then went quiet for a while as we built an all-new server architecture better suited to powering the types of product propositions that we look forward to releasing over the next six months.
An iceberg seen from off the coast of Graham Land in Antarctica
The first of the releases built on our new platform - the all-new BBC iPlayer 2.0 site - went live on June 25, just over a month ago.
Like an iceberg, the BBC iPlayer 2.0 site is the bit "above the water". The new site is doing well, but to me more important than the site itself is the ability that our new architecture (the invisible mass below the water) gives us to deliver innovative and world-class new features, even faster than we've been shipping them so far.
Okay, now on to the announcement: H.264.
The video you see in BBC iPlayer today is encoded using the On2 VP6 codec, at a bitrate of 500Kbps. The On2 codec (a video compression technology from a company called On2) is pretty much the standard for video delivery over the internet today. It's optimised for moderately low data rates (300Kbps to 700Kbps, rather than the 2Mbps to 4Mbps needed for HD content), and low CPU usage, allowing it to work reasonably well on older computers. In short, On2 VP6 is the video workhorse of the internet.
When we went live with streaming in BBC iPlayer back in December last year, we needed to make some decisions about the streaming technology to use. Adobe Flash with On2 VP6 codec was the obvious technology choice (it's also used by YouTube and most other video sites), because evryone already had Flash installed, meaning that nobody would need to install anything in order to use BBC iPlayer - an important criterion.
Choosing a bitrate was more difficult: too low and the resulting video quality would be unacceptably poor; too high (with corresponding higher bandwidth) and people on lower bandwidth connections would experience buffering problems - ie, pauses in playback that reduce your viewing pleasure. I think we chose well, hitting the right spot between quality and bitrate and giving a good quality playback experience, at least when playing back within the playback "window" on the BBC iPlayer web site. However, the full-screen experience was less than optimal. As the majority of BBC iPlayer users watch BBC iPlayer in full-screen mode, this is clearly something that needs to be addressed.
H.264 is a high-performance video compression technology - the new kid on the block, so to speak. It's actually been around for a few years, but only recently have a few things come together to make H.264 usable by us. Compared to On2 VP6, H.264 delivers sharper video quality at a lower data rate, but requires more CPU power to decode, particularly on older machines, and the user needs to have the latest version of Flash installed.
Back in December of last year, relatively few people had installed the Flash player needed to play H.264 content; now almost 80% of BBC iPlayer users have it. More machines now have graphics cards with H.264 hardware acceleration. Additionally, Level3, a content distribution network (CDN) is now able to stream H.264 content to ISPs in the UK, and the content encoding workflows that we use (Anystream and Telestream) are now able to support H.264.
Actually, when I say that our content encoding workflows are now able to support H.264, that's not quite correct yet. Our compression technology suppliers are frantically working on getting the preferred MainConcept H.264 compressor into their software, something they're hoping to complete in the next week or two. In the meantime we're using the QuickTime codec, which produces results that are acceptable, but not as good. So it seems we're really on the leading edge here.
Anyway, to cut a long story short, the good news for those looking for video quality improvements in BBC iPlayer is that, starting this week, we're going to be encoding our content in H.264 format at 800Kbps. Additionally, our media player now supports hardware acceleration in full-screen mode, giving a greatly improved image at lower CPU usage than before.
Along with the change to H.264, the soundtrack in our video programmes is changing to AAC+, another new compression technology that delivers better sound at a lower bitrate. The bass is deeper, the treble tighter, the overall effect is a noticeably better listening experience, particularly if you listen with headphones or hook up your computer to your TV or home sound system.
However, given that we're on the (leading) edge here, with our CDN network and video compression partners only now being able to support our requirements, we're going to play it safe and introduce H.264 in two phases:
In the first phase, starting this week, we're going to create our content in both On2 VP6 and H.264 format, and provide a button to let you choose which works best for you and your internet connection, Normal or High:
Initially, the default will continue be On2 VP6, which will remain the choice for users on slower internet connections. However, if your internet connection speed is 1Mbps or higher, try the "HIGH" H.264 version.
In the second phase, we're going to add automatic bitrate detection, so that our media player software automatically chooses the right version for your computer and internet connection speed - we'll likely introduce this auto-detection feature in September. This will make it as easy as possible for all users to get the best quality of service possible with the equipment they have.
Initially the H.264 option will only be offered to people who have the latest version of Flash installed, and will be offered incrementally as new content rolls out through our encoding chain. We'll also be making a number of tweaks and enhancements over the coming weeks as our video compressor suppliers deliver more software updates, so look out for further improvements over the next few weeks.
On a different topic, the BBC iPlayer has been shortlisted for three British Technology Awards - Best Home Entertainment, Most Indispensable Technology and Best Online Technology. The winners are determined by popular vote here. All votes for BBC iPlayer are much appreciated :)
Anthony Rose is Head of Digital Media, BBC Future Media & Technology.