IMSC-Rosetta: A new era for subtitle formats – bridging broadcasting and streaming

IMSC-Rosetta: A new era for subtitle formats – bridging broadcasting and streaming

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IMSC-Rosetta: A new era for subtitle formats – bridging broadcasting and streaming

Robert Cranfield

Wed 04, 10 2023

IMSC-Rosetta: A new era for subtitle formats – bridging broadcasting and streaming

Rob Cranfield, Director Media Supply Chain Technology, Warner Bros. Discovery 

In the realm of media, delivering subtitles consistently across various platforms has posed challenges. Warner Bros. Discovery (WBD) identified the pressing need for an innovative subtitle format. This format should seamlessly suit both conventional TV broadcasts and contemporary streaming services. Historical subtitles have been fragmented, existing in diverse proprietary and generalized formats. However, none of these formats proved universally fitting for all content types and languages.

In response, WBD partnered with Yella Umbrella, a company with proven extensive experience in subtitle formats and linguistic support going back over 30 years. Their joint endeavor aimed to create a fresh subtitle file format that resolves these complexities. After evaluating multiple options, they selected IMSC V1.2 as a foundational framework. While IMSC V1.2 provided the framework, its inherent variability posed challenges in achieving consistent and reliable outcomes. The heart of the matter was devising a method to harness TTML’s potential while enforcing a standardized representation of subtitle text, timing, and style information, thereby eliminating the complexity of adapting generic TTML files for diverse purposes.

The outcome of this collaboration culminated in the IMSC-Rosetta subtitle file format. This innovation draws inspiration from IMSC V1.2, while streamlining the structure for clarity and uniformity. This rectifies challenges tied to XML-reliant formats, well known for their intricacy and incompatibility. IMSC-Rosetta champions ease of use, rendering parsing, modification, and creation accessible without necessitating mastery of exhaustive technical minutiae of XML and TTML.

IMSC-Rosetta files showing mixed English, Arabic and Japanese including vertical presentation in the Stellar editor from Yella Umbrella.

IMSC-Rosetta retains the full spectrum of features seen in alternative subtitle formats, encompassing color, outlines, boxing, and text placement. Its distinctiveness lies in its definitive construction, facilitating seamless translation across disparate formats and languages via the IMSC-Rosetta standard. For entities adhering to proprietary formats, transitioning to IMSC-Rosetta guarantees minimal feature loss and significantly reduced development efforts, in contrast to the more intricate IMSC or TTML routes.

IMSC-Rosetta’s versatility extends across a range of applications, serving as a solution for authoring, delivery, interim storage, and archiving. It stands out for catering to translation requirements, preserving the nuance created by subtitlers – often compromised during conversion processes.

The necessity for IMSC-Rosetta emerged from observations concerning the slow adoption of TTML. Despite its merits, complexities in implementation spawned an array of TTML-based formats that operated effectively as proprietary standards due to the demanding nature of implementation and the variable interpretations of standards. Existing implementations often overlooked subtleties that elevate the viewer’s experience, as compatibility with distinct media and streaming platforms took precedence.

IMSC-Rosetta emerges as a remedy for these disparities, streamlining development while setting forth a pathway to quality within a comprehensible, standards-compliant subtitle file format. Unlike many TTML-derived derivatives with limited reusability, IMSC-Rosetta catalyzes change by offering seamless conversion to ‘proprietary’ IMSC formats.

This is especially timely ahead of the roll-out of Max, WBD’s streaming service that is currently live in the U.S. and is launching in European countries early next year with launches also planned for LatAm and Asia-Pacific.

Commencing September 8, 2023, IMSC-Rosetta will be accessible to all. The complete specification, coupled with samples, example source code, and a public wiki, will be accessible at Queries, observations, and contributions are warmly welcomed through the issue-raising channel on the platform.

In an industry perpetually evolving, IMSC-Rosetta provides a method to store and deliver consistent, high-quality subtitling across languages and distribution channels.

By providing a single universal standard format, IMSC-Rosetta helps the whole media industry supply quality localized content while reducing production costs.

IMSC-Rosetta is the result of over 18 months work primarily by Simon Hailes of Yella Umbrella and Robert Cranfield of WBD, with input and review from various industry partners.


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