NCast Presentation Recorder Reference Manual
9.3. M
EDIA
P
LAYERS
The MPEG-4 format used by the Presentation Recorders is an industry-wide standardized format which
multiple client players support.
For PCs with properly configured software the playback process will be quick and easy.
However, if a customer is having difficulty, common problems to check include:
The client player has not been installed or is not at the latest revision level.
A codec required for playback has not been installed. Windows Media Player does not natively
support MPEG-4 files and needs a plug-in to be installed to properly decode Presentation
Recorder streams. Contact NCast Corporation for details concerning availability of its MPEG-4
plug-in.
Some other application has associated with one of the above file extensions.
Firewalls (either in the laptop/desktop or externally) are blocking access to the required RTSP or
UDP ports.
The network being used is not multicast enabled and multicast connectivity is being requested.
The network path between the client and the server is bottlenecked and unable to sustain the
packet flow required for smooth, continuous playback. Wireless links, very commonly, do not
have the throughput required for media streaming.
The machine does not have enough processing power or memory to sustain continuous
playback. Some modern PC have a “power-saving” mode, and there have been instances where
the machine goes into power-save mode during playback, crippling the capacity of the machine.
Other activities in the machine (including hidden spyware or Trojans) are consuming so much
CPU time that the media player is unable to get the processing cycles required for correct
playback. Even some active web pages can consume nearly 100% of the CPU.
The audio devices set for the media player have not been configured correctly.
The audio has been muted.
9.4. C
LOSED
-C
APTION
S
UPPORT
Section 508 of the Rehabilitation Act of 1973, is an amendment to a law requiring that electronic and IT
technology provided by agencies of the Federal Government be accessible to both employees with
disabilities and to members of the public with disabilities. The Section 508 requirement has been adopted
by a growing number of university and university systems, including all California State University
colleges.
1
Video and/or multimedia products also fall under the standard, by including requirements for
captioning of multimedia products such as training or informal multimedia productions. Captioning, or
video descriptors must be able to be turned on or off.
2
NCast’s Presentation Recorder product lines fall
under the category of video and/or multimedia products, and are thus required to implement closed
captioning for appropriate compliance.
9.4.1. Real-time sub-titles and chapters
There does not appear to be a single, widely adopted standard for recording timed-event information for
use either in sub-titles or chaptering. Some client players use various forms of .txt files and others use
.xml files.
The Presentation Recorder implementation has adopted one format which is simple to use and has some
existing support in the open-source community and works with several players.
The format is an ".srt" text file type which is described here:
http://en.wikipedia.org/wiki/SubRip
New serial commands have been added to receive text information and automatically create ".srt" files
during a recording.
These files will be:
1 http://www.calstate.edu/accessibility/section508/section_508_FAQs.shtml
2 http://www.section508.gov/index.cfm?FuseAction=Content&ID=11
NCast Corporation
Revision 1.0
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