Re: WebVTT, Regions and live streams.

Bill - 

thanks so much for raising these issues. I donıt have answers, but I will
add that from Viacomıs perspective, replicating the live aspects of
CEA-608/708 with rollup and paint-on support and screen-clearing (EDM) is
important in allowing is to leave CEA-608/708 in the past and move onto
modern formats such as TimedText and webTTT.

thanks,
Glenn

Glenn Goldstein
SVP, Chief Technology Convergence Officer
Tel: (212) 846-3210
Email: glenn.goldstein@viacom.com






On 9/18/15, 4:34 PM, "May, Bill" <bill.may@mlb.com> wrote:

>Hello, 
>
>My name is Bill May; Iım an engineer at MLB Advanced Media looking into
>how to expand Closed-Captions into a world-wide solution.
>
>Weıre looking for a user experience similar to closed captions; the
>ability to have 1 word/letter at a time displayed, support for roll-up
>type caption for both VOD and live (event and linear) presentations.  We
>use HTTP Live Streaming (HLS) as our video protocol.
>
>CEA-708 captions are are one possible solution, but we believe that it
>will get harder as we add more languages.  Weıd like to unbundle the
>captions from the other media.
>
>So, it will come as little surprise that Iım thinking of webVTT.
>
>With the later versions of the specification, WebVTT has done an
>excellent job of translating 608/708 and the properties required into
>webVTT using the region attributes, but only for a completed VOD type
>presentation.
>
>Solutions like HLS and DASH use a duration based segmentation to provide
>(near) live streams.  When we need to provide webVTT cues for a live
>stream, the direction isnıt very clear.  Specifically:
>
>1). How to handle a EDM (clear screen).
>2). what to do at the end of a segment/beginning of the next when the
>closed caption line spans the segment.
>
>case 1: (EDM)
>When we use the region syntax, I have been assuming is that each cue gets
>a start time, and an end time that encompasses the 16 seconds maximum
>time that the closed caption specifications state.
>
>That way, as the captions are added, the oldest ones will roll out of the
>region, even if they have time left.  If captions arenıt added, they have
>(Please correct me if my assumption of the region is wrong).
>
>However, that doesnıt let me enter a clear screen command.  Thereıs no
>way to change the end time of those earlier cues.
>
>One possible solution for this is to add a bunch of short lived cues with
>non-breaking space, but I do not believe that this is acceptable due to
>the background artifacts.
>
>case 2 (cues that overlap segmentation)
>As for the segmentation, assume we have the following: Assuming a region
>with 2 lines, and letıs say we want to push out each word every 3/4
>second (by using the timing mechanisms).  (Iıve left out any cue settings
>to make it a bit clearer)
>
>00:00:00.000 ‹-> 00:00:17.500
>Caption <00:00:00.750>Line <00:00:01.500>1
>
>00:00:03.000 ‹> 00:00:22.000
>Caption <00:00:03.750>Line
><00:00:04.5>2<00:00:5.25>Longer<00:00:6.000>extended
>
>If we need to provide segmentation at 5 second intervals, the
>segmentation process does not have the words ³Longer² and ³Extended²;
>they havenıt been entered by the captioner.  It also doesnıt know what
>the end time should be, as it should be 16 seconds from the end of the
>last word.  
>
>Creating a new cue that starts for ³Longer² and ³extended² will cause the
>³Caption Line 2² part to scroll; we want it to continue on the same line.
>
>Iıd like to know if there is a clear solution to these problems, and if
>not, if additions to the specification can be added to handle these cases.
>
>Thanks,
>Bill May 
>MLB Advanced Media

Received on Monday, 21 September 2015 19:04:10 UTC