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Encoding

Basics

Once your recordings have been digitised you will need to encode the material, ready for streaming across a network. Although the file in your computer is digital and can be read by other computers, it is simply too large to be streamed over the net. Therefore you must put the data through a process of encoding or compression.

Encoding removes information from your data - your media file - that would not be noticeable to the viewer when the file is played online. Within digital files there is a huge amount of information held within the pixels that make up the image. By removing some of these pixels, the data that the human eye will not notice, you can reduce the overall size of the media file.

When you remove information from a media file, during the compression stage, you may be able to retrieve that information in the decompression stage. This is called Lossless compression. With Lossless compression, no data will be lost and you can view a complete image. This may be useful if you are planning to edit the image in some way or you need a high quality print. A more familiar type of compression or encoding will be Lossy. Lossy is the opposite of Lossless in that information extracted will not reappear in the decompression stage. The more you save a file, which has been compressed using a Lossy compressor the greater the degradation on your image will be. Of course, the more information you retain in your image, the more information you will have on your computer, hence more memory and processing time required. Lossless compression is used primarily in the production of archives where you need to retain as much information as possible. For streaming content online and for general viewing the Lossy option will be the preferred choice. This will allow a large reduction in the amount of data being transferred to the user.

The process of encoding material is the process of applying a codec (compressor/decompressor). A codec is a software component that configures information from a compressed file to a decompressed file enabling the viewer to watch your media. You can select which codecs you wish to use when you are encoding your material. Some codecs will come as part of your encoder package, but in some instances you will need to pay for a codec on top of your encoding package. The Sorenson video codec for example is not a free product and you will need to buy a licence in order to use this particular product.

To look at the MAAS Encoding specification as an example:

An encoder can be software or hardware and the type of encoder you select will reflect the amount of work you are intending to compress. For example, a commercial facility house dedicated to producing a large amount of encoded material may invest in a specific hardware encoder. Such equipment will have significant processing power and be capable of turning around a vast amount of material very fast, often for commercial use. If your through-put of material is more sporadic and does not rely on a quick turn around you may find a software encoder will be suitable for your needs.

A commonly used software tool is Cleaner. Cleaner 6 (available for Mac industry-standard media mastering and encoding solution for Apple Macintosh) and Cleaner XL (industry-standard media mastering and encoding solution for Windows) are popular and user friendly web media authoring tools which are widely available. Although Cleaner is not free, you are guaranteed a very cost-effective tool with built in specifications for easy creation of media files for use on the web. Cleaner has a Wizard option for the first time user, so you can familiarise yourself with the techniques. The three main developers of streaming media, Microsoft, RealNetworks and Apple have created their own encoding software, which you can read more about on their specific websites.

For more information, go to the following websites:

Formats

MPEG

The MPEG, named after the Moving Picture Experts Group, is a media compression file standard, which has been used as a bench mark for quality for a number of years. The Moving Picture Experts Group is a working group under the Internal Standards Organisation (ISO) who are in charge of the development of international standards for compression, decompression, processing and coded representation of moving pictures and audio. MPEG originated with MPEG1 and was followed by MPEG2, MPEG4 etc. The standard continues to develop with broadcasting needs for a quality picture at a low data rate and a range of flexibility for the developing interactive community. The MPEG1 format can be played on any media player and is a safe file format to use if you are thinking of multiple use.

The MPEG Group - an overview
  • MPEG1: can be read by all the standard players; RealPlayer, QuickTime and Windows Media. The format is a standard for transmitting video over satellites and cable television.
  • MPEG2: familiar format for DVD production.
  • MPEG3: the popular audio format is a subset of MPEG - the audio layer.
  • MPEG4: based on the Apple QuickTime technology. Web multimedia delivery standard, however some work, on extensions in specific domains, is still in progress. MPEG4 is a versatile and reliable format that can be used by different software developers. This compatibility makes MPEG4 the staple file format for multimedia applications and to stream good quality audio-visual information at relatively low bit rate.
  • MPEG7: formally named Multimedia Content Description Interface, aims to create a standard for describing multimedia content data.
  • MPEG21: primarily developed to answer the need for infrastructure standardisation within multimedia.

ASF

Microsoft developed its own streaming format the ASF (Active Streaming Format). ASF was introduced in conjunction with the developing MPEG4 standard. Most streaming media for windows will have an asf extension.

MOV

Developed by Apple and a popular streaming and downloadable format across the web. QuickTime files are recognisable by the extension .mov.

AVI

AVI or Audio/Video Interleaved is a Microsoft-specified format for saving audio and/or video clips, referred to by Windows as "Video for Windows." You can play the files through the Media Player in Windows or through many popular browser plug-in multimedia players.

WAV

WAV or Wave Form Audio (files with the .wav extension) are digital representations of sound and typically take up a large amount of space to store.

RealVideo and RealAudio

If you are using RealVideo or audio from RealNetworks as your media clip the extension of your file will be .rm or .ra.

DV

The term DV is used in two different contexts. Firstly it is a generic term for digital video. Secondly, it is the name for formats which store compressed video at either 50 or 25 megabits per second. There are a variety of formats including Consumer DV, DVCAM, DVC, DVC-PRO and DVC-PRO50. The higher quality formats are mainly found in high end broadcast equipment. It is also worth mentioning that a device capable of DV does not necessarily have any digital outputs.