❝ The IMSC provides broadcasters and service providers with an international footprint to deliver subtitles and captions services to
the world in a single format .❞
❝ As ATSC 3.0 has selected the IMSC1 , DASH integration is important to allow the IMSC1 to interoperate between broadcast and Internet-delivered content . This is the first time in the history of closed caption and subtitle technology , where there is an open
source implementation available to facilitate interoperability .❞
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March 2017 CREATION 15
captions multilingual
accu racy , adhering to the conventions and formatting guidelines of each broadcaster ; for example , how to denote multiple speakers , annotate off-screen comments and work out reading speed .
“ The key is to think from the perspective of someone who is deaf or hard-of-hearing , and ensure that they can enjoy the content equally to those without a hearing impairment .”
Another key challenge , according to Dr Green , is ensuring that both subtitling and closed captioning are delivered in a “ platformagnostic ” format so that they can be “ repurposed quickly and costeffectively ”. This is notably crucial for content producers who are looking to distribute their content on online platforms , he adds .
The entertainment landscape is
❝ The IMSC provides broadcasters and service providers with an international footprint to deliver subtitles and captions services to
the world in a single format .❞
— Dr Pierre-Anthony , Editor , Internet Media Subtitles and Captions 1.0 ( IMSC1 )
shifting due to the growth of online video platforms , such as Netflix and Amazon Prime Video , which are capable of delivering content on a global scale via the Internet . To improve accessibility of the delivery of subtitling services for online video content , the World Wide Web Consortium ( W3C ) has published a new global standard — the Timed Text Markup Language ( TTML ) Profiles for the Internet Media Subtitles and Captions 1.0 ( IMSC1 ).
Dr Pierre-Anthony Lemieux , editor of the IMSC1 , elaborates : “ Subtitles and captions are an integral part of the entertainment experience , and supporting multiple regional formats increases acquisition and distribution costs . A standard is therefore desirable .
“ The IMSC1 provides broadcasters and service providers with an international footprint to deliver subtitles and captions services to the world in a single format . These operators can therefore author , take delivery , store and deliver subtitles in a single format .”
Claiming that the IMSC1 represents a “ significant milestone ” in an effort to establish a single global standard for subtitles and closed captions , David Ronca , director of encoding technologies at Netflix , says that the IMSC1 would allow the company to achieve its goal in providing the “ highest quality caption and subtitles at a global scale ” while preserving the creative intent of the assets .
Also a member of the W3C , Netflix is fully committed to supporting the IMSC1 as the “ preferred model ” for subtitle delivery into the Netflix ecosystem , Ronca adds , as well as in the next steps of enhancing the IMSC1 to be a complete global subtitle standard , for example , by adding support for Japanese subtitles .
The IMSC1 features “ forced subtitles ” that can carry text both for hard-of-hearing viewers and translation of subtitles , enhanced text alignment and padding that
❝ As ATSC 3.0 has selected the IMSC1 , DASH integration is important to allow the IMSC1 to interoperate between broadcast and Internet-delivered content . This is the first time in the history of closed caption and subtitle technology , where there is an open
source implementation available to facilitate interoperability .❞
— Mike Dolan , Chairman , SMPTE Technology Committee on TV and Broadband
supports captioning styles in Europe , images in addition to text-based subtitles , as well as reference fonts and character sets to improve rendering fidelity . It is also integrated with the IMSC1 Hypothetical Render Model that allows document complexity to be measured at the time of authoring while ensuring it can be played downstream .
Commenting on the development of the IMSC1 , Zoo Digital ’ s Dr Green says : “ The IMSC1 is the result of more recent efforts to harmonise the exchange of timed text information in the hope that this will be the one format that all industry partners can agree on . Designed specifically as an interchange format across subtitle and caption delivery applications worldwide , the IMSC1 would be a good choice as it has the support of leading industries bodies to facilitate interoperability and encourage good practice .”
The harmonisation of these technical guidelines for online video captions and subtitles was a colla borative effort among members of the W3C Timed Text Working Group , a team comprising global experts and external organisations , including the
European Broadcasting Union ( EBU ) and the Society of Motion Picture and Television Engineers ( SMPTE ).
Mike Dolan , chairman of the SMPTE Technology Committee on TV and Broadband , says : “ The IMSC1 profile simplifies TTML to meet the closed caption feature of the Consumer Technology Association ( CTA ) -708 standard for digital TV ( DTV ) closed captioning , as well as subtitle requirements for theatrical and distributed media such as Blu-ray .”
He further reveals that an IMSC1 reference decoder has been developed under open source , and is currently added to the dynamic adaptive streaming over HTTP ( DASH ) reference decoder , which will form an open source reference for any DASH-based deployment , such as ATSC 3.0 .
Dolan concludes : “ As ATSC 3.0 has selected the IMSC1 , DASH integration is important to allow the IMSC1 to interoperate between broadcast and Internet-delivered content . This is the first time in the history of closed caption and subtitle technology , where there is an open source implementation available to facilitate interoperability .”
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