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LAST-MODIFIED:20260204T174529Z
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DTSTART:20240331T210000
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UID:e3212ca5-bf9f-4c8f-858c-fe24b1569440
DTSTAMP:20260204T174529Z
SUMMARY:Revisiting in-band text tracks in MediaSource Extensions
DTSTART;TZID=Etc/UTC:20250326T210000
DTEND;TZID=Etc/UTC:20250326T220000
DESCRIPTION:https://www.w3.org/events/meetings/e3212ca5-bf9f-4c8f-858c-fe24
 b1569440/\n\nThe [MediaSource Extensions (MSE)](https://www.w3.org/TR/medi
 a-source/) spec has included in-band text tracks since the first published
  working draft\, but that part of the spec have lacked browser adoption fo
 r a very long time.\n\nRecently\, WebKit has added experimental support fo
 r in-band text tracks in MSE. Work on this has highlighted a number of cha
 llenges in bytestream formats and the MSE specifications.\n\nThe purpose o
 f this breakout session is to gather together\, discuss those challenges a
 nd come to agreement on the direction to tackle them in the MSE specificat
 ions.\n\n**Goal(s):**\nClarify some finer points about how in-band text tr
 acks in MSE should work and define next steps for improvements in the spec
 ifications.\n\nAgenda\n\nBasic familiarity with MediaSource Extensions is 
 expected for attendees.\n\nTo make the session easier to follow\, the sess
 ion will start with a very brief introduction of specific formats that wil
 l be relevant for the discussions\, such as:\n\n* WebVTT in ISO BMFF (MP4)
 \n* WebVTT in WebM: S_TEXT/WEBVTT and D_WEBVTT/kind\n\nAfter that introduc
 tion\, a number of topics will be discussed. For each topic there is at le
 ast one question that we hope to answer.\n\n* Cues vs samples vs MSE coded
  frames\n  * Should the MSE spec refer explicitly to cues\, and if so\, ho
 w?\n* Would it be desirable for MSE to have a concept of sparse stream gap
 s? Could the bytestream formats allow it?\n  * The SourceBuffer with only 
 a text track problem\n  * Use cases other than text tracks\n* Embedded CEA
 /CTA-608/708 signalling\n  * Would support of embedded CTA-708 in MSE be d
 esirable?\n  * What would be the best way to accomodate embedded text trac
 ks like this?\n* Cues across segment boundaries: ISO BMFF\, WebM and proce
 ssing in MSE\n  * Should the MSE spec mandate cues are extended instead of
  duplicated?\n  * Should the MSE spec mandate that when cues are extended\
 , they are updated and "oncuechange" is emitted\, instead of removed and r
 e-added?\n* MSE WebM bytestream: are the current WebVTT representations ac
 ceptable for MSE?\n  * Should we advocate for any specific improvements?\n
   * Should the MSE WebM bytestream spec be updated to refer to any specifi
 c WebVTT representation?\n\nInterested parties are encouraged to call atte
 ntion to any other existing challenges with in-band text tracks in MSE and
  the related technologies.\n\nThis list is not final and given the limited
  time\, it may not be possible to cover all the topics\, much less agree o
 n answers for most of the questions. These discussions can still serve as 
 a starting point for later work in the working groups.\n\n**Materials:**\n
 - [slides](https://ntrrgc.github.io/w3c-breakouts-2025-mse-text-tracks/)\n
 - [slides archived in zip on w3.org](https://www.w3.org/2025/Talks/mse-tex
 t-tracks-breakouts-2025.zip)\n- [recording](https://www.w3.org/2025/03/bre
 akouts-day-2025/recordings/recording-14.html)\n- [Session proposal on GitH
 ub](https://github.com/w3c/breakouts-day-2025/issues/14)
STATUS:CONFIRMED
CREATED:20250314T182308Z
LAST-MODIFIED:20260204T174529Z
SEQUENCE:6
ORGANIZER;CN=W3C Calendar;PARTSTAT=ACCEPTED;ROLE=NON-PARTICIPANT:mailto:nor
 eply@w3.org
LOCATION:Marigold
CATEGORIES:W3C Breakouts Day 2025,Breakout Sessions
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