DTV Closed Captioning Bulletin

1
DTV Closed Captioning Bulletin

• The work of CEA R4.3 WG1 TG2
• or
• Why more examples will make a better standard
• Charlie Dieterich
• Sarnoff Corporation
• Princeton, NJ USA

2
Specifications are Complex!

• MPEG 2 Video is 200 pages
• EIA 708 B is 92 pages
• Each paragraph can have several compliance
  points!
• The window size is specified in numbers of
  character rows and character columns for all
  display formats (169, 43, etc.). For all
  display formats, 15 is the maximum character row
  count and 32 is the maximum character column
  count. (EIA 708 B 8.4.6)

3
How To Improve Implementation Consistency

• MPEG Video
• Distribute software that implements all feature
  of the standard
• EIA-708 B
• Provide clear and consistent explanations of
  features
• Provide examples of syntax element use
• Provide discussion of options where the standard
  allows flexibility

4
Why We Must Act Now...

• First encoder implementations only use a subset
  of features
• First decoder implementations must support all
  mandated features

5
Why We Must Act Now

• Subset works, but...
• What if other parts of the Spec are not
  implemented consistently?
• Spec is changed to remove those features
• or
• Spec implementation needs sunset provisions to
  allow faulty implementations to go away

6
How do we make sure implementations are
consistent?

• Step 1
• Create a document that includes discussion of
  technical points
• Especially the obscure ones!
• Step 2
• Include example streams and desired result
• EIA 708 B has some examples
• We need lots more examples

7
Types of Examples

• Task Group 1 MPEG transport streams with caption
  sequences
• Most useful for decoder testing
• Task Group 2 Syntax sequences with the expected
  result
• Useful for encoder and decoder code development

8
Plan and Timetable

• Develop a list of issues to be clarified
• Have several engineers look at each paragraph
• Develop a set of standard answers in the form of
  a CEA Bulletin
• Have it done by this summer.
• Preliminary versions restricted to Working Group
  members
• August 1st R4.3 Meeting Final Release