RTP Payload for TTML Timed Text
draft-sandford-payload-rtp-ttml-02

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A/V Transport Payloads Workgroup                             J. Sandford
Internet-Draft                          British Broadcasting Corporation
Intended status: Informational                          February 4, 2019
Expires: August 8, 2019

                    RTP Payload for TTML Timed Text
                   draft-sandford-payload-rtp-ttml-02

Abstract

   This memo describes a Real-time Transport Protocol (RTP) payload
   format for TTML, an XML based timed text format for live and file
   based workflows from W3C.  This payload format is specifically
   targeted at live workflows using TTML.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 8, 2019.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions, Definitions, and Abbreviations . . . . . . . . .   2
   3.  Media Format Description  . . . . . . . . . . . . . . . . . .   3
     3.1.  Relation to Other Text Payload Types  . . . . . . . . . .   3
   4.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Payload Data  . . . . . . . . . . . . . . . . . . . . . .   4
       4.2.1.  TTML Profile for RTP Carriage . . . . . . . . . . . .   5
   5.  Payload Examples  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Congestion Control Considerations . . . . . . . . . . . . . .   9
   7.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  10
     7.1.  Media Type Definition . . . . . . . . . . . . . . . . . .  10
     7.2.  Clock Rate  . . . . . . . . . . . . . . . . . . . . . . .  14
     7.3.  Mapping to SDP  . . . . . . . . . . . . . . . . . . . . .  14
       7.3.1.  Examples  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Appendix A.  RFC Editor Considerations  . . . . . . . . . . . . .  18
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   TTML (Timed Text Markup Language)[TTML] is a media type for
   describing timed text such as closed captions (also known as
   subtitles) in television workflows or broadcasts as XML.  This
   document specifies how TTML should be mapped into an RTP stream in
   live workflows including, but not restricted to, those described in
   the television broadcast oriented EBU-TT Part 3[TECH3370]
   specification.

2.  Conventions, Definitions, and Abbreviations

   Unless otherwise stated, the term "document" is used in this draft to
   refer to the TTML document being transmitted in the payload of the
   RTP packet(s).

   Where the term "word" is used in this draft, it is to refer to byte
   aligned or 32-bit aligned words of data in a computing sense and not
   to refer to linguistic words that might appear in the transported
   text.

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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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