ACTION-30: Skim the work done by the media pipeline tf

Hi Bin and group,

Based on my action item (ACTION-30):
  http://www.w3.org/community/tvapi/track/actions/30

I've skimmed the Requirements document generated by the Media Pipeline
TF of the Web and TV IG at:
  http://www.w3.org/2011/webtv/wiki/MPTF/MPTF_Requirements

There are the following 11 requirements in the document, and I think
this could be a good check list for our requiremnts document at:
 https://www.w3.org/community/tvapi/wiki/Main_Page/Technical_Requirement

and the table at:
 https://www.w3.org/community/tvapi/wiki/Main_Page/Requirements_Mapping

Delivery of Television Services:
--------------------------------
- R1. Combined "Main + Description" Audio Track
- R2. Key Metadata Types
- R3. Handling of In-band Tracks
- R4. Content Authorization Parameters
- R5. Content Authorization Failure

Adaptive Streaming of Media Content:
------------------------------------
- R6. Adaptive Bit Rate Format Support
- R7. Additional Media Parameters
- R8. Additional Media Feedback and Errors

Content Security and Digital Rights Management:
-----------------------------------------------
- R9. Security and Digital Rights Management Identification
- R10. Content Protection Parameters
- R11. Content Protection Feedback and Errors

Also I think it would be useful for us to revisit the Media Accessibility
User Requirements:
  http://www.w3.org/TR/2014/WD-media-accessibility-reqs-20140814/

For example, we might want to consider how to handle:
- described video
- text video description
- extended video descriptions
- clean audio

Thanks,

Kazuyuki