BTC640/Video

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Lecture

Textbook chapter: 6

Since TV took off video has been one of the best ways to deliver information to consumers. Like other presentation technologies it's better for some kinds of information than others, and also like other presentation technologies there is lots to learn about it.

Because the technology is quite complex we will only get an overview of video in this course, without going into too much detail, but you need to know some basics at least.

Codecs and Containers

Video is encoded and decoded using a codec. The format is a digital representation of the data (like PNG, WAV, BMP), and the codec is a program following rules for creating and displaying it (like libpng).

Video is rarely used without audio, but the two are separate technologies that are combined into one by placing them into the same container and synchronising their playback. This is the main reason that a container is not the same as a codec.

Examples of containers:

  • AVI
  • MPEG
  • Matroska (mkv)
  • Quicktime (mov)
  • 3GP
  • Flash (flv)

Each of these containers contains video in one of a few formats, for example:

  • MPEG-1
  • MPEG-2
  • MPEG-4
  • H.263
  • H.264
  • Theora

as well as audio in one format or another.

The decision which container and format to use is usually dictated by the tools available, the distribution channel, and the size/quality of the result.

Channels and Interfaces

There are two big categories here: analog and digital. With video the differences between the two are similar to the differences between analog and digital audio, though unlike analog audio - analog video is lossy.

Here are the most popular channels and interfaces for video:

Analog channels

  • Component video: three cables with an RCA jack each. If audio is required - a fourth cable (usually also RCA or double-RCA for stereo) is used.
  • VGA cable/connector: the most common video-out connector in a computer. This is also component video. Though it usually comes out of a computer - it does not carry a digital signal.
  • S-Video: one cable with a DIN connector. Only two channels instead of 3 as with component thus lower quality. The cable does not carry audio, usually the separate audio cable has TRS connectors.
  • Composite: a single cable with an RCA jack. All the information goes over this single channel, which makes it the lowest quality of the three. If audio is required - a fourth cable (usually also RCA or double-RCA for stereo) is used.

Digital channels

  • DVI: a specification for digital transmission of video, and also the common name for a connector. No audio. Interestingly a DVI cable also carries an analog signal for the same video.
  • HDMI: an interface that includes digital video, digital audio, CEC, and even ethernet. Mini HDMI and micro HDMI are also becoming popular, used on smaller devices such as smartphones.

RF channels

  • Coaxial cable (like cable TV) actually transmits radio signals over a wire, which is why it's heavily shielded. It can be used for both analog (like traditional cable TV) and digital (like high-speed internet) signals, often at the same time.
  • Broadcast TV uses some of the available RF spectrum to broadcast video signals as far as they will go. This used to be completely analog transmissions, but more recently digital transmissions started beeing used. This is a heavily regulated distribution channel, you cannot simply set up your own.

Video on the Web

A few years ago it became possible to put videos on the web by using a Flash container, which worked great because almost everyone had a recent version of the flash plugin installed.

More recently with development of HTML5 it became possible to embed non-flash videos on webpages using the <video> tag. Unfortunately that specification does not mandate use of a particular container and codec, so support for the tag varies with different browsers.

Links

Lab

Shoot some video, edit it, put it on a webpage.

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