HDTV - what you should know before buying

HDTV Is HereWe've been waiting over a decade for HDTV, and now that it's finally available, there's as much confusion in the marketing as there is clarity in the images. If you're won over by the promise that your favourite films and sports will wow you all over again, and you buy a new TV with an HD-ready sticker on it for Christmas, how much more will you need before you actually see an HD image on the screen? Here's the current state of the game.HD BasicsHD stands for high definition; a higher resolution than the 'standard' TV pictures we're used to. It doesn't have to be broadcast in digital format but usually is, in part because that allows the large picture to be compressed for broadcast; HDTV uses either MPEG2 or MPEG4.Confusingly, HD covers a range of resolutions; currently an image can have 720 or 1080 vertical lines in 16:9 widescreen format, resulting in pixel resolutions of 1280x720 and 1920x1080. Unlike standard TV, pixels aren't being stretched to fit the 16:9 image. You won't see letterboxing, except on extra-wide movies like Lord of the Rings; if you're watching HD content that's been produced in the older 4:3 aspect ratio you'll get black bars on the side instead.HD also covers both interlaced images - the system used in CRT screens to paint alternate lines of the image - and progressive scan, the system used by LCD and plasma flat-screen TVs. Most HD content is produced as interlaced, and there is some discussion over the quality difference between 1080 interlaced (1080i) and 1080 progressive (1080p). This is complicated by the fact that interlaced content has to be de-interlaced for display on a progressive screen, which degrades the image. in fact, 720p content may look better than de-interlaced 1080i on a progressive screen, though unless you have a large screen and good content to start with you may not see much difference anyway. 1080p content would certainly look better, but this takes a lot of bandwidth to broadcast and won't be available any time soon. Blu-Ray discs will generate 1080p images, as will a PlayStation 3 (although the content may be scaled up by a factor of four so don't expect fantastic quality for everything from a PS3). Xbox 360 produces 1080i output, as does the first generation of HD-DVD, though future players will support 1080p.Standard television may look better when it's de-interlaced on a progressive HD screen because motion may look smoother, but poor-quality images will be more noticeable too. Normal DVD content is of good enough quality that it looks better on an HD screen, especially if the DVD player has its own progressive scan processor.HD content tends to have 5.1 channel Dolby Digital AC-3 surround sound, rather than the stereo sound of standard TV.What You Need For HDTo view HD content, you need a screen that can display the full resolution of the HD content. Some HD ready screens, especially lower-priced plasma screens, can only display 720 lines, so 1080 content has to be down sampled. You also need an HD receiver, for broadcast content, an HD set-top box for cable or satellite HD content, or an HD-DVD or Blu-Ray player for HD content on DVD. VIIV PCs and current Windows Media Center PCs can receive HDTV with the right tuner. Some TVs labelled as "HD ready" have the receiver built in - since March 2006 all 25-35" sets sold in the US must include an HD tuner - but before you pay extra for it, check how the HD content you want to watch is going to be broadcast.To connect HD devices together you don't use SCART or S video. Although some HD equipment lets you connect via component video or even FireWire, the main connector is High Definition Multimedia Interface (HDMI). This interface supports high-definition sound too: 8-channel 192kHtz uncompressed audio, as well as Dolby Digital and DTS. HDMI 1.3 will support the new Dolby TrueHD and DTS-HD lossless digital audio formats. Confusingly, manufacturers can choose which features of HDMI to implement; if you want a DVD-Audio or SACD connection, check if the HDMI connection on the set you're considering implements it.For connecting a PC or a high-definition DVD player or set-top box that decodes copy-protected content, you may need High-bandwidth Digital Copy Protection (HDCP). This is a system that applies DRM to a DVI or HDMI connection. The "protected video path" in Windows Vista uses HDCP connections to let you play DRM content but not pirate a copy. Creators of Blu-Ray and HD-DVD discs can choose to set a flag that only lets you play the content in HD via an HDCP connection; if you connect it to a system without HDCP you get a downsampled version instead.Recording HDTVYou can record an HDTV broadcast on a standard VHS, DVD or PVR recorder, but you'll only get standard resolution. This will be better than the same content recorded from a standard TV source, but it's not HD. HD PVRs are coming out, but HD takes up a lot more disk space. Blu-Ray and HD-DVD will have recording formats also, but they'll be expensive for a long time. You can record HD content on a Windows Media Center PC too. There is an HD version of the DivX codec that you can record HD content in; even though they're MPEG4, standard DivX recordings aren't HD.HD ContentIn the US, many viewers can get HD content over the air through a standard TV antenna (especially if you adjust it to the best angle for your area). Not all channels broadcast in HD and not all the programs on an HD channel are in HD, but currently Fox, ABC and SPN broadcast 720p content, and NBC, CBS, HBO-HD, TNT and several HD-specific channels broadcast in 1080i.In the UK you can get HD by cable from NTL/Telewest or by digital satellite from Sky (including some programs on the free-to-air BBC channels available by digital satellite without a Sky subscription). A small Freeview trial in London broadcasts HD versions of BBC, ITV, Channel 4 and Five (though only a few programs are showing in HD on the channels) to HD-capable digital set-top boxes. The full service isn't likely to start until the analogue channels are switched off (currently estimated to be sometime between 2008 and 2012), freeing up extra bandwidth.You don't have to get HD content by broadcast. Films will be available on DVD in HD, in both Blu-Ray and HD-DVD formats. IPTV services often include HD channels, and in the UK, BT is launching a service offering HDTV over broadband for pay-per-view content. Microsoft has an HD codec for Windows Media Player, Apple has an HD codec for QuickTime and you can download movie trailers in HD. Expect more HD downloads of programs from pay-for services in both formats, as well as DivX HD, but also expect large files that could take several hours to download at current broadband speeds. High resolution means great quality - but large files!