What is Hi-definition (HD) video?
Introduction
A simple definition of a broadband internet connection is anything faster than dial up (56Kbps). Thus a simple definition of hi-def (HD) video might be anything with more lines (or pixels) than standard definition (SD).
As with broadband, there are a wide variety of HD video formats, camcorders and televisions. In this article we will attempt an overview of the most popular HD video formats.
HD provides a sharper and more detailed picture than SD (stop me if I'm going to fast!). Technical definitions are somewhat unhelpful so what you need to do is go down to your local dealer and see a demonstration of a Blu-Ray>HDMI>HDTV setup. Like many others I was initially skeptical about HD, having been perfectly happy with SD DVD quality and not being a big TV watcher. But now I know better.
In my opinion, a well mastered 1080i Blu-Ray disc (with H264 compression) looks enormously better than free to air TV transmissions (usually heavily compressed MPEG-2), perhaps 4-6 times sharper, and 2-3 times better than SD DVD.
It really is a substantial improvement and one you can more easily appreciate if you switch from HD back to SD. I thought something had gone wrong with my TV!
HD for web site and multimedia authors
At the time of writing the vast majority of broadband services available are not fast enough to permit real-time streaming of SD video, let alone HD. Also, authoring Blu-Ray (HD) DVD discs is problematic as desktop computer software packages, and indeed optical drives, have not yet fully embraced HD DVD authoring. Therefore, the vast majority of web designers and multimedia authors cannot fully take advantage of the new technologies yet.
However, there seems little point in investing in and using SD technologies when the future is clearly HD, and there is plenty of evidence that video sourced from an HD camcorder looks better when compressed for the web than SD video compressed the same. Garbage-in garbage-out, as they say. Also, HD video created today will be useable in the future, and it looks as though self-financed HD video (film, drama, comedy etc) distributed on the web is going to have a bright future once a practical financial model is established. There are plenty doing it for free now.
HD content sources
Here are the current primary ways to view HD content ...
- Over the air TV broadcast to a HD tuner and HDTV or HD projector
- Cable TV broadcast to a HD tuner and HDTV or HD projector
- Satellite TV broadcast to a HD tuner and HDTV or HD projector
- From a stand-alone Blu-Ray DVD disc player to an HDTV or HD projector
- From a games console (PS3) fitted with a Blu-Ray DVD disc player to an HDTV or HD projector
- From a HD video camcorder to an HDTV or HD projector
- From a computer graphics card to an HDTV or HD projector
- From the internet to set top boxes (such as Apple TV) to an HDTV or HD projector
HD video formats
The quality of most video formats are defined by 4 criteria ...
- The number of frames (or fields) per second (fps).
- Whether each frame is "drawn" with the interlaced or progressive scan method (more on this later).
- The vertical (number of lines) and horizontal resolution of each frame.
- The bit-depth of its colour system.
Here is a comparison chart showing the primary SD and HD standards.
| SD formats | HD formats | ||||
|---|---|---|---|---|---|
| Resolution | Frames per second | Aspect ratio | Resolution | Frames per second | Aspect ratio |
| 720 x 480 (NTSC) - interlaced & progressive | 29.97 | 3:2 | 720p (1280 x720 progressive) | 24-60 | 16:9 |
| 720 x 576 (PAL) - interlaced & progressive | 25 | 5:4 | 1080i (1920x1080 interlaced) | 24-60 | 16:9 |
| 1080p (1920x1080 progressive) | 24-60 | 16:9 | |||
| 2160p (3840×2160 progressive) - cinema 4K standard | 24-60 | 16:9 | |||
From my research it is not clear what frame rates are most commonly used for HD formats, and although up to 60fps is possible I believe that most consumer delivery (broadcast TV and Blu-Ray) is closer to SD rates (ie 29.97 and 25 fps).
Progressive scan and interlacing
Video formats use one of 2 ways to create each frame.
Interlaced
Each frame of video is displayed in two passes (or fields). The first draws the even number horizontal lines and the second the odd number horizontal lines. This happens fast enough to deceive the eye into seeing one complete frame/field but does cause some "flickering" of the picture. Interlaced video has a lower data rate than progressive and is therefore used for low bandwidth broadcasts. More on interlacing here.
Progressive
Progressive scan draws all the lines in a frame/field in a single pass and is widely considered to produce a superior picture to interlaced, more film like and less video like.
Codecs
HD pictures are usually compressed for broadcast or optical disc delivery typically using an MPEG-2 codec, but preferably an MPEG-4 variant such as the superior H264 codec used for most Blu-Ray content. More on video codecs here.
The audio channels can remain uncompressed or utilise a wide range of codecs including AAC, MP3 and AC3. Of course 5:1 surround sound is supported.
Colour bit depth
A non technical (or technical!) explanation of the improvements in HD colour depth are beyond this writer. Can I just say that HD colour depth exceeds SD?!
HD devices
Here are some primary HD devices ...
- HDTV
- HD capable set top box
- HD tuner
- HD video camcorder
- Blu-Ray DVD player
- HD enabled games console
- Internet set-top-box / computer system (eg Apple TV, Mac and iTunes)
HDTV's
Native resolution and upscaling
It is important to understand that a (HDTV) display will have a native resolution, ie the physical number of pixels. My own Sony Bravia 32" LCD TV has a native resolution of 1366 horizontal by 768 vertical. Incidentally the 26", 27" and 40" models in the range have the same native resolution.
Therefore, when playing a PS3 game (typically at 720p resolution) my TV must "upscale" the picture to fit my TV (720 lines to 768 lines). Similarly, when I play a 1080p Blu-Ray DVD film, presumably my TV must "downscale" the picture to fit (1080 lines to 768 lines). This re-scaling process typically loses 3-4% of the potential picture quality (ie not usually noticeable).
Generally, you require a TV of at least 42" to watch 1080p HD content at native resolution (pixel for pixel) without upscaling. I bought my Sony TV because its Bravia picture/upscaling engine is widely regarded as one of the best (and because it was cheap!).
HDMI
The preferred method for connecting HD devices such as Blu-Ray players, multi-channel amplifiers and HDTV's is the HDMI cable which can carry HD pictures and multi-channel sound digitally between devices.
In conclusion
There are many more things to say about HD, many of them highly technical, but for most digital artists and multimedia developers the information presented on this page, and the type of HD camcorder to buy, are the most important things to know. At present there are many HD camcorder formats recording to many different types of media using many different codecs (!!!!). Check out this page for the latest we have on the subject.
Related downloads
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