- From: Goldstein, Glenn <glenn.goldstein@viacom.com>
- Date: Mon, 21 Sep 2015 19:03:41 +0000
- To: "May, Bill" <bill.may@mlb.com>, "public-texttracks@w3.org" <public-texttracks@w3.org>
- CC: "Zurat, Bill" <Bill.Zurat@mlb.com>
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