ABSTRACT
The advances in digital technologies have transformed the broadcasting industry dramatically. Traditional analogue techniques are gradually being replaced with digital systems in almost every aspect of a broadcasting environment. Only a few decades ago all audiovisual (AV) content was analogue and Edit Decision Lists (EDLs) were nearly the only digital content produced.1,2 AV raw material has been stored on analogue tapes, and information pertaining to its content kept separately, often in a non-digital form. Today, digital media have found their way into editing,
production and archiving systems. With improved compression algorithms and increased bandwidth digital content is increasingly used for transmission and will indeed replace traditional broadcasting in the near future. Storage and material exchange is one of the many areas
where the use of digital content is of advantage. For instance, a variety of physical devices can be utilised for storing digital data, such as optical discs, digital tapes or standard computer hard discs. Once in the computer domain, data may be easily transferred using standard network protocols such as TCP/IP,3,4
or may be even used for Internet broadcasting using the realtime protocol RTP/RTSP.5,6
Computer systems store data in binary form, called a file. Typically, the actual raw data within a file are stored in a structured way. Additional information, in many cases located at the top of a file (hence called a ‘header’), is provided to allow data access and processing. This type of information is called metadata. A file format specification contains a complete definition of both data structure and content. Many different multimedia file formats are already avail-
able.7 Not all of them are of use in broadcasting, where high image and sound quality is required. As a consequence, formats such as MPEG and DV have been created to meet those AV quality requirements. However, optimising storage by designing appropriate compression techniques is only part
of a digital content and workflow solution. To take full advantage of digital technologies, content has to be efficiently accessible and manageable. To facilitate this, additional descriptions and unique identification is needed. This type of content-related metadata is known as ‘descriptive’ metadata (as opposed to ‘structural’ metadata describing the digital material). ‘Rich’ metadata contains both structural and descriptive metadata. Considerable efforts have been undertaken to define satisfactory descriptive metadata models such as P/Meta8 and MPEG-7.9 Some of these efforts have gone into the formats described below. The provision and inclusion of rich metadata is an essential requirement for any new data format in broadcasting. Over the years, manufacturers have been designing their
own digital formats to accommodate broadcasters’ needs. This has been an acceptable solution for single self-contained systems. However, most broadcasters wish to choose their equipment and systems from different manufacturers. In addition, digital content is no longer produced, edited and transmitted by one organisation alone. Rather, the process may involve external departments and studios. Therefore, exchanging digital content is an essential part of any broadcasting workflow today. To exchange material from different origins and in different formats requires, often costly, transcoding processes and equipment. To resolve this issue the broadcasting industry has been
working on defining and standardising storage and data exchange file formats. As a consequence, new standards have emerged. To give a complete account of all existing proprietary standards is beyond the scope of this chapter. Instead, an introduction to the most recent and relevant formats is given. The selection includes:
. The General Exchange Format (GXF).
