ISSUE-317: IMSC should not require frame alignment

IMSC should not require frame alignment

IMSC should not require frame alignment

State:
CLOSED
Product:
TTML IMSC 1.0
Raised by:
Nigel Megitt
Opened on:
2014-05-22
Description:
IMSC 1.0 §4.4 [1] currently requires temporal quantisation of media times to frame display times. This rule comes into play when times are not expressed in frames, and therefore the same document may apply to a range of related media objects covering different frame rates. In the case when frames are used the document can only be displayed alongside media of the same frame rate so there's no need for the frame alignment expression.

This approach prevents implementations from changing caption display at screen refresh rate quantisation and enforces quantisation based on the encoded video frame rate. This means that if a low frame rate video is provided, e.g. quarter rate which could be around 6 frames per second, the effective word reading rate may be increased to the point where text becomes hard to read.

Consider a streaming environment in which there is enough network capacity to provide audio and captions but the video experience is badly impacted: in this case it must be permitted that the implementation continue to present captions alongside the audio regardless of the frames of video that are displayed.

I propose a solution to this problem that implementations SHALL display captions as temporally close to the media time specified as the display device permits, independent of video frame rate.

Note that where frames are used in media time expressions this reduces to exactly the current behaviour.

[1] https://dvcs.w3.org/hg/ttml/raw-file/ea1a92310a27/ttml-ww-profiles/ttml-ww-profiles.html#synchronization
Related Actions Items:
No related actions
Related emails:
  1. {minutes} TTWG Meeting 24/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-24)
  2. {agenda} TTWG Meeting 24/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-23)
  3. {minutes} TTWG Meeting 17/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-17)
  4. Revised Editor's Draft of IMSC (from pal@sandflow.com on 2014-07-16)
  5. {agenda} TTWG Meeting 17/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-16)
  6. {minutes} TTWG Meeting 10/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-10)
  7. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from John.Birch@screensystems.tv on 2014-07-10)
  8. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from John.Birch@screensystems.tv on 2014-07-10)
  9. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-07-09)
  10. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-06-20)
  11. {minutes} TTWG Meeting 19/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-19)
  12. RE: {agenda} TTWG Meeting 19/6/2014 (from mdolan@newtbt.com on 2014-06-18)
  13. {agenda} TTWG Meeting 19/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-18)
  14. RE: {agenda} TTWG Meeting 12/6/2014 (from mdolan@newtbt.com on 2014-06-12)
  15. Re: {agenda} TTWG Meeting 12/6/2014 (from pal@sandflow.com on 2014-06-11)
  16. Re: {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  17. Re: {agenda} TTWG Meeting 12/6/2014 (from pal@sandflow.com on 2014-06-11)
  18. Re: {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  19. {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  20. RE: {agenda} TTWG Meeting 5/6/2014 (from mdolan@newtbt.com on 2014-06-04)
  21. {agenda} TTWG Meeting 5/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-04)
  22. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-28)
  23. {agenda} TTWG Meeting 29/5/2014 (from nigel.megitt@bbc.co.uk on 2014-05-28)
  24. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-27)
  25. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from glenn@skynav.com on 2014-05-24)
  26. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-23)
  27. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
  28. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-23)
  29. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
  30. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-23)
  31. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
  32. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-23)
  33. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
  34. RE: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-23)
  35. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
  36. RE: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-22)
  37. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-22)
  38. RE: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-22)
  39. Re: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-22)
  40. RE: ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-22)
  41. ISSUE-317 (IMSC should not require frame alignment): IMSC should not require frame alignment [TTML IMSC 1.0] (from sysbot+tracker@w3.org on 2014-05-22)

Related notes:

Addressed in https://dvcs.w3.org/hg/ttml/diff/fb65791a33af/ttml-ww-profiles/ttml-ww-profiles.source.html per 10/7 meeting

Pierre-Anthony Lemieux, 17 Jul 2014, 04:16:54

Display change log ATOM feed

David Singer <singer@apple.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, Chairs, Thierry Michel <tmichel@w3.org>, Philippe Le Hégaret <plh@w3.org>, Atsushi Shimono <atsushi@w3.org>, Staff Contacts
Tracker: documentation, (configuration for this group), originally developed by Dean Jackson, is developed and maintained by the Systems Team <w3t-sys@w3.org>.
$Id: 317.html,v 1.1 2019/11/12 10:06:57 carcone Exp $