ANSI SCTE 27:2016 pdf download.Subtitling Methods for Broadcast Cable.
NOTE: This document is identical to SCTE 27 2011 except for informative components such as the title page, NOTICE text, headers and footers. No changes have been made to any text in the document beyond this point, other than headers and footers.
1.1 Purpose
This document detines a standard for a transmission protocol supporting multilingual subtitling services to augment video and audio within MPEG-2 multiplexes.
1.2 Organization
The sections of this document are organized as follows:
Section 1 — Presents the scope.
Section 2 — Lists compliance notation and terms.
Section 3 — Lists applicable documents
Section 4— Provides an overview of subtitling system design.
Section 5 — Specifies the subtitle message format.
2 COMPLIANCE NOTATION
“SHALL” This word or the adjective “REQUIRED” means that the item is an absolute requirement of this specification.
“SHALL NOT” This phrase means that the item is an absolute prohibition of this specification.
“SHOULD” This word or the adjective “RECOMMENDED” means that there may exist valid reasons in particular circumstances to ignore this item, hut the full implications should be understood and the case carefully weighted before choosing a different course.
“SHOULD NOT” This phrase means that there may exist valid reasons in particular circumstances when the listed behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.
“MAY” This word or the adjective “OPTIONAL” means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it

2.1 Terms, Acronyms and Abbreviations
2.1.1 Terms
The following terms are used throughout this document:
message: A sequence of bytes comprising a data structure defined in this Standard. All messages begin with the table_ID and end with the CRC_32 field. Messages are carried in non-PES streams; their starting points within a packet payload is indicated by the pointer_field mechanism defined in the ISO/IEC 13818-I Systems document.
section: A message comprising a portion of an ISO/IEC 13818- 1-defined table, such as the Program Association Table (PAT), Conditional Access Table (CAT), or Program Map Table (PMT). The term conforms to MPEG terminology, hut since it applies primarily to the delivery of table structures, the more appropriate term “message” is used to refer to non-table oriented data structures such as, for example. the subtitle message.
program element: A generic term for one of the elementary streams or other data streams that may he included in a program.
program: A collection of program elements. Program elements may be elementary streams. Program elements need not have any defined time base; those that do have a common time base and are intended for synchronized presentation. The term “program” is also used in the context of a “television program” such as a scheduled daily news broadcast. The distinction between the two usages should he understood by context.
service: ISO/fEC 13818-1 uses the term “program” to refer to a collection of program elements without regard to time. In this Standard, the term “service” is used in this same context to denote a collection of elementary components. Usage of the term service clarifies certain discussions which also involve the notion of the term program in its traditional meaning (in. for example, the statement “A video service carries a series of programs”).ANSI SCTE 27 pdf download.