N.B. Editors note: As Chris Cornwall noticed last week there was a premature announcement of BBC iPlayer going HD. But now it's ready, and Anthony has the full details.

Internet video used to be, and for the most part still is, a grainy, lower quality version of the video that you're used to seeing on your TV, and subject to stops and starts that you wouldn't expect or tolerate from broadcast television.

The good news is that today BBC iPlayer takes a major step to address that quality gap, with some programmes now available in HD, and all programmes now also available in a new SD-quality stream that's pretty close to TV quality. As of today, iPlayer's standard definition video quality should be as good as most Freeview channels, plus you'll now be able to stream or download BBC programmes in high definition without need for a set top box.

Along with the introduction of these new higher quality formats, we're also adding a new larger video playback window, adding adaptive bitrate technology to automatically deliver the best quality video that your internet bandwidth can support, and adding a diagnostics page that lets you easily test your internet connection speed.

Finally, we're taking our cross-platform iPlayer Desktop download application out of Labs and ending our use of peer-to-peer technology.

It's a major release, the most significant since the current iPlayer site went live in July last year. Much of the new technology in this release sits 'beneath the hood', so let's take a look at the new features in more detail:

iPlayer goes HD

Good news for those with fast computers and fast internet connections: BBC iPlayer now delivers some of your favourite BBC programmes in HD. The HD proposition in iPlayer follows the HD content availability on the BBC HD channel, so we're starting with about 40 hours of HD content per week, which will grow over time.

HD has been a long time coming to iPlayer, so you might be interested in the back story:

We first began investigating HD in iPlayer over a year ago. The BBC HD Channel quality controllers have high standards and insisted that for us to label content as "HD" it had to be true HD - i.e. 720p or above with no obvious encoding artefacts. No cheating (as some other video sites do) labelling anything upwards of 800x600 as HD - our HD needed to be at least 1280x720.

That meant using H.264 and an encoding bitrate of 3Mbps or greater (we actually settled on 3.2Mbps as our preferred HD bitrate). However, since many people won't have an internet connection that can stream 3.2Mbps reliably, we wanted to make HD available for download as well. Trouble is, a year ago our download manager was Windows-only, and we were determined to only release HD when we had a solution that allowed our Mac and Linux users to download them as well. Additionally, a year ago too few people had a version of Adobe Flash that could play H.264, which meant many users would need to install a software update in order to access our content - something we're keen to avoid.

The good news is that as of today the various pieces are in place for going live with HD: Our new cross-platform download manager allows Windows, Mac and Linux users to download HD, everyone has a version of Flash that can stream HD, and our HD channel now has more content available.

It should be noted that glitch-free HD playback requires a fairly recent computer with a decent graphics card - older computers won't be able to handle the CPU-intensive decompression & rendering and may drop frames, leading to jerky playback. To get the best HD experience always play back in full-screen mode, and if you don't have enough bandwidth to stream try downloading instead.

So, look for the new BBC HD Channel in iPlayer, then go full-screen to enjoy the HD quality. Or, why not take this opportunity to connect your computer to your (HD-capable) TV set and enjoy HD on a nice big screen.

Note that HD programmes are about 1.5 gigabytes per hour of video, so you might want to check your internet package, particularly if you're on a 3G connection, to see if you're on a bandwidth-capped plan and, if so, how many hours of HD content you can stream or download before you reach the monthly limit for that plan.

New resizable media player

Back in December we introduced in iPlayer Labs (the testing ground for new iPlayer ideas and features) the ability to change the size of the video playback window.

iPlayer Labs users told us via their feedback (which we hugely value and which influences our product design decisions) that they loved the idea, asking overwhelmingly for this feature to graduate from Labs. In Labs we tested three video player sizes - you told us that the smallest and largest sizes hit the spot.

So today the ability to resize the video player window graduates from Labs and is available to all iPlayer users.

New high quality 1500Kbps video format

Finally, BBC programmes should look as good on your computer as they do on your TV, even if you don't choose the HD option.

If you select the new large video window size, iPlayer will automatically switch to using our new 1500Kbps 832x468 video format. When you switch to full-screen mode, iPlayer will continue to use the 1500Kbps stream for a playback experience that's close to TV quality.

Programmes that you download using iPlayer Desktop will now also use this new 1500Kbps format, making downloads now close to TV quality as well.

Regular video streams get a boost too

In addition to introducing a new 1500Kbps SD quality format, we've also shifted our default video quality up a notch, so that our existing High Quality (800Kbps H.264) format now becomes the default used in the smaller video playback window size. For programmes without fast movement played back on a small computer screen the quality of that 800Kbps format is pretty good, which means that as of today our baseline video quality takes a big step up.

Adaptive bitrate, phase one

You might be thinking... the baseline stream has changed from 500Kbps to 800Kbps... what if I don't have enough bandwidth to stream 800Kbps (or for that matter our new 1500Kbps streams)?

The good news is that this iPlayer release also includes the first phase of our adaptive-bitrate technology, such that iPlayer will now automatically switch to a lower bitrate stream if it detects that you don't have enough bandwidth to play the preferred version. For example, if you're happily playing the 1500Kbps stream when your partner at home also decides to watch an iPlayer programme on their computer and you don't have enough bandwidth to support both streams, then iPlayer will automatically drop down to 800Kbps, and then down to 500Kbps, as needed.

In this first phase of our adaptive bitrate system, once iPlayer has dropped down to a lower bandwidth stream it will stay with that lower bandwidth version for the rest of the programme you're watching. Over the coming months we'll enhance that behaviour to allow iPlayer to automatically ramp up and down between available versions every few seconds to match your available bandwidth.

For users on bandwidth-capped internet connections or who otherwise might want to override the adaptive bitrate system and use only our lowest bandwidth (500Kbps) stream, we've provided an option to do so (right).

New internet speed diagnostics page

With the availability of our new 1500Kbps and HD streams we thought it a good time to add a diagnostics page to help you see what bandwidth you're getting from your ISP, and also help us better understand average bandwidths that our users are getting, including allowing us to analyse the bandwidth available from different ISPs by time of day, etc.

Our new diagnostics page - https://www.bbc.co.uk/iplayer/diagnostics - looks at first glance similar to others you may have seen at speedtest.net and elsewhere, but it's significantly more sophisticated than other speed test sites we've seen.

Most speed test sites measure the speed taken to download a small file over HTTP. That's a good number to know if you're trying to measure your HTTP download speed, but what we and our users are more interested in is the ability to stream an iPlayer programme - and that means measuring RTMP streaming protocol speed, and from the specific locations where our servers are located. Accordingly, our diagnostics page performs a total of four tests: The first tests the download speed from our BBC web site servers, the next three tests measure the Flash RTMP streaming speed from each of three major content distribution networks (Akamai, Level3, Limelight), giving us excellent visibility into overall network throughput and allowing us to shape future design decisions accordingly.

iPlayer Desktop out of Labs

Three months ago we released iPlayer Desktop, our new Adobe AIR-based cross-platform download manager. Initially we made iPlayer Desktop available to Labs users only, allowing early adopters to try it out and give us feedback.

Many thanks to all those Labs users who sent us valuable feedback - we read them all - you'll find many of the bugs you mentioned have been fixed, and many of the ideas and suggestions have either been incorporated into the latest version or are on the to-do list for future release.

Today iPlayer Desktop graduates out of Labs, replacing our existing download manager as our new cross-platform download platform. Windows, Mac and Linux users can now download iPlayer programmes, including in HD, for offline playback.

As of today, we're no longer using P2P to distribute our content, or use your upload bandwidth- all content is now either streaming or direct HTTP download from our servers. If you're a user of our existing BBC iPlayer Download Manager, you can continue to use it to play back files that you've previously downloaded, but all new downloads will be via iPlayer Desktop, so feel free to go ahead and uninstall BBC iPlayer Download Manager (look for that entry in Add/Remove Programmes). Note that Sky Player and 4OD use the same Kontiki technology as our existing BBC iPlayer Download Manager, so if you've installed their download managers you may find that some shared Kontiki components remain after uninstalling ours.

Download to view on your TV

Although they've not yet caught on in a big way, Windows Media Extender devices provide a way to play back downloaded movies and songs on your TV set. Made by companies including Linksys, D-Link, NetGear and Zyxel, plug one end of these devices into your home network (or connect via wi-fi) and the other end into your TV set and/or audio system, and you can then browse and play files shared on your home network by any PCs running Windows Media Centre. Many of these devices have HDMI outputs,1080p upscaling and SP-DIF audio output to your 5.1 system, providing a high-quality way to play back downloaded programmes on your TV.

User feedback told us that a popular use case for downloading iPlayer programmes was to play them back in Windows Media Centre or via these Windows Media Extender devices. We have good news for these users: We're now making those same WMV files available for direct download, with no need to install any software - just look for the More Downloads option (right), then download the file, save it to your desktop or Windows Media Centre library, and play it out as you wish, including moving it around your home network, playing it back on other devices in the house, etc.

Now working on... iPlayer 3.0

Over the next couple of months we'll have a few more iPlayer releases with additional features, but the iPlayer team is now focussing on the next-generation of the iPlayer site - we call it the iPlayer 3.0 release - coming this summer - though it's early days it's looking really exciting - stay tuned for more info as development progresses.

Anthony Rose is Controller, Online Media Group and Vision, Future Media & Technology.