What is Hi-definition (HD) video? by Matt Ottewill (June 2008)

There are at present 2 categories of video ...

  1. SD (standard definition) - which uses technologies such as Freeview TV broadcast, miniDV camcorders and DVD video discs.
  2. HD (high definition) - which uses technologies such as HD satellite and cable, iTunes, and Blu-Ray discs.

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 back from HD back to SD. I thought something had gone wrong with my TV!

blu ray logoHD 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 delivery

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 6 criteria ...

  1. The number of frames (or fields) per second (fps).
  2. Whether each frame is "drawn" with the interlaced or progressive scan method (more on this later).
  3. The vertical (number of lines) and horizontal resolution of each frame.
  4. The bit-depth of its colour system.
  5. The codec employed to compress it for storing or transmission.
  6. The file format in which they are stored (technically this does not alter quality but is another way in which formats differ).

Because a camcorder/camera is where video is first captured and compressed, the codecs they use often determine the codec used throughout the complete edit. There is a comprehensive round-up of current camcorder and codec technologies here.

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.

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?!

Codecs & file formats

The production workflow for HD can be complex and use a variety of file/codec formats. Unlike DV which was an agreed standard between manufacturers, there is little or no standards for how HD video should be compressed and stored. Some camcorder manufactures have co-operated and developed joint file/codec formats (such as the Sony/Panasonic AVCHD format) but most have not. Also, it is not always obvious what codec a given manufacturers camcorder file format is employing.

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.

There are essentially 3 "stages" of codec use. Here are some examples ...

Codecs used by camcorders/cameras to store video
AVCHD (Advanced Video Codec Hi Definition)
Red camera format
Panasonic AVC-intra
DVCPRO-HD
XDCAM EX
HDV
etc
File/codecs formats used by editing software 1. Same as camcorder

2. Intermediate codecs such as Apples Final Cut Pro family of ProRes codecs (there are 5 types) which allows HD video to be handled in SD sized files.
etc

3. Editing codecs which require camcorder formats to be transcoded for editing
File/codecs formats used for broadcast / delivery AVCHD
MPEG-2
MPEG-4 / H.264
Flash video
QuickTime
AAC, MP3, AC3, PCM (audio formats)
etc

 

Because a camcorder/camera is where video is first captured and compressed, the codecs they use often determine the codec used throughout the complete edit. There is a comprehensive round-up of current camcorder and codec technologies here.

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)

Sony Bravia TVHDTV'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 plugHDMI

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. Because a camcorder/camera is where video is first captured and compressed, the codecs they use often determine the codec used throughout the complete edit. There is a comprehensive round-up of current camcorder and codec technologies here.