Streaming - A Practical Guide to Video and Audio Compression - page 349

ingly large. This has prompted companies to found organizations to help control this com-
plexity and agree on some common profiles.
The standardization process is driven by several factors. Some de facto standards
evolve first as a result of a new innovation by a proprietary service that has been devel-
oped by a single company. This leads to competitive products from other manufacturers,
and soon there is sufficient interest that a standards body forms a working group to
develop an open-standard-based alternative. Then the manufacturers of proprietary play-
ers recognize this and add that open standard to their players. Gradually, the proprietary
formats decline in use, since none of them guarantees 100% penetration. At least that is
how it should work in an ideal world.
With video-compression standards, certain functionality is defined as being manda-
tory and other capabilities are grouped into bands of features that are likely to be useful
as the sophistication of a service increases. Basic streaming of simple rectangular content
might be defined as a base level, while multiple streams of non-rectangular video are
something that a basic player does not need to support but a premium player might well
be able to play back.
This leads to the standards working groups' defining some profiles of functional-
ity that player manufacturers must support in order to be able to claim compliance.
Within those profiles, different levels of performance specifications are addressed.
For example, a basic functionality profile might define that a single rectangular video
be played, but a variety of different sizes and bit rates might be defined as alternative
levels.

20.5.1 Internet Streaming Media Alliance Profiles

The Internet Streaming Media Alliance ( ISMA ) defines some constraints on performance
and bit-rate requirements to facilitate streaming services. Two profiles were published
some time ago known as Profile 0 and Profile 1. At the beginning of 2005, the version 2.0
draft standard was released, which adds Profiles 2, 3 and 4.
There is a degree of compliance between ISMA and MPEG, for example. The MPEG
standards are mapped to digital video broadcasting (DVB) and Digital Television Group
(DTG) specifications and standards for television defined by the Advanced Television
Systems Committee ( ATSC ) and the European Broadcasting Union (EBU). With the VC-1
codec under consideration, SMPTE should also be included. The version 2.0 ISMA stan-
dard further integrates the work with 3GP and DVD next-generation formats and pro-
vides more DVB harmonization.
Refer to Appendix H for technical details of the ISMA Profiles 0 to 4.
The previous version of the specification was 1.0.1, which also includes the version
1.0 Authentication and Encryption standard. A version 2.0 document has been released for
comment and should be approved by the spring of 2005.

ISMA Web site: http://www.isma.tv/