Digital Video basics

by EngageMedia August 20, 2012

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Player Software

The operating system used by members of your audience will have a default media player installed – Windows Media Player for PC, Quicktime Player for Mac and for many Linux distributions it will be Mplayer. Other proprietary media players that will handle different types of video are RealPlayer and iTunes.

VLC (VideoLAN Client) is a cross-platform FLOSS media player that is designed to be a universal video player. VLC will play back most formats and codecs without the need to download additional software modules, and will also play back DVDs and VCDs. As VLC is GPL licensed it is possible to re-distribute the program along with your video. VLC offers many other features including streaming.

Compression

Most consumer NLE (non-linear editing) applications such as Premiere, Final Cut Pro or Cinelerra (for Linux) edit and render DV (Digital Video) files natively – either in SD (standard definition) or in the newer HD (high definition) formats. Even standard definition DV has a high fixed bit rate (the amount of data streamed over time). DV has a bit rate of 36 megabits per second or around 4 minutes of video per Gigabyte, resulting in files too large for transport on the web. It is necessary to compress these video files to make them smaller, in a format that will be compatible with your audience’s player software.

Your options for compressing video include exporting directly from the timeline of your video editing application or by using a FLOSS or shareware encoding application such as Virtual Dub (Windows), MediaCoder (Windows), ffmpegX (Mac OSX), or gtranscode (Linux). Features to look for in an encoding application include batch encoding so you can line up many files to encode at once, settings you can save and re-use, and the more support for various codecs and formats the better. A great resource containing guides for encoding is http://www.videohelp.com/

Codecs

A codec (which stands for compression-decompression) is a software module that contains algorithms used by encoding or playback software to encode or decode video and/or audio information.

Popular proprietary codecs include Windows Media Video and Sorenson 3 for Quicktime. Depending on your audience’s access to the Internet, operating systems and technical abilities it may be in some cases a good idea to offer your video in one of these codecs in addition to a FLOSS codec. A good resource for comparing codecs is the doom9 website.

One codec option that is becoming increasingly popular for playback within Internet browsers is Flash video. FLV or SWF files containing video are well suited to being embedded in a web page, as they only require the Flash browser plug-in for playback – which most Internet users already have without needing to download any additional software.

Open source video codec alternatives include Ogg Theora or the XviD codec. XviD is a high quality codec and is the most widely supported open source option available. It is relatively simple for most people to watch as many players have native support for XviD. It is also easier than Ogg Theora to encode, as there are more applications available to encode it.

You can read more about tools available for creating and distributing FOSS codecs in the report "FOSS Codecs for Online Video: Usability, Uptake and Development".

The most highly regarded and widely supported open source audio codec is the LAME mp3 codec, which can be incorporated within many different container formats (see below).

The future of video codecs lies with those built to the new H.264 or AVC standard that forms part of the MPEG-4 specification (see “Standards” below). There is a GPL-licensed application of H.264 called x264. This is a codec to watch – many people are using it already but it is still in early development and uptake is still limited as compared to XviD. It is also a much more highly CPU-intensive codec, both when compressing files and decompressing them in player software – which means it uses more computer processing power. It is therefore not recommended for use on older less powerful computers – which must be considered when thinking about your audience.

Container Formats

A container format is the wrapper code around the audio and video streams in a file to synchronise the two for playback. It can also contain other information such as chapters, sub-titles and metadata. Examples of container formats are ASF (the Windows streaming format), Quicktime (Apple’s .mov format), 3gp (a type of MPEG4 format for mobile phones) and AVI (an early Windows format still widely in use). Each of these formats can only support certain codecs for each audio or video stream. The open .ogg format can contain codecs such as Vorbis (audio) and Theora (video). The XviD codec is used within the AVI format.

Standards

Video compression standards, such as the MPEG1, MPEG2 and MPEG4 standards set by the Motion Picture Experts Group, are a set of rules that video codecs and formats must be designed to adhere to. This standardisation, as in any other area of engineering, allows manufacturers and software designers to anticipate the kind of video, audio and other information that their software or hardware will have to process.

The MPEG4 standard contains several parts including Advanced Simple Profile (MPEG4 Part 2) that contains elements implemented in codecs such as XviD, 3ivX and DivX. A new more advanced part of the MPEG4 standard, known as H.264 (MPEG4 Part 10), is set to become the major standard used by the next generation of High Definition DVD and Television, as well being used for video conferencing and other online video delivery.

Mobile Devices

Encoding to certain specifications will allow users to watch video on their mobile devices such as a mobile phone, PSP or video iPod. Conversely it is possible to record video with many mobile phones or digital cameras these days, often in the 3gp format. Users can then transfer these video files to a computer and upload them onto the Internet. These files are already highly compressed and therefore do not require further encoding and are most useful when uploaded along with supporting material such as text and images as the video and audio quality is quite low.

 

 

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