Media profile: CMAF IMSC1 Text ('im1t')

"Captions/subtitles using the TTML IMSC1 Text profile defined in CMAF."

For a Provisional media profile:

Name/company of designated proponent

Chris Poole/BBC

Note: The Designated proponent is responsible for providing all deliverables necessary to meet the WAVE Media Profile requirements.

Market relevance

Meet at least one of the following conditions.

Codec with existing market relevance

1. Digital Media Service Providers (at least 3):

2. Digital Media Playback Devices available in the market (at least 5):

Codec with WAVE membership support

1. Device manufacturers which are WAVE members (at least 2): Microsoft, Apple, TP Vision

2. Content providers which are WAVE members (at least 2): BBC, Comcast, MovieLabs, HBO

3. Other Wave members (at least total of 6 including the above members): Akamai, Qualcomm

Note: A WAVE member company self-declares at the time of voting whether they wish to be considered a device manufacturer, a content provider or other.

Open standards

List the standard for the media profile: ISO/IEC 23000-19 Common Media Application Format

Note: To meet the WAVE Media Profile ‘open standard’ requirement, the media profile in question must have been developed following an open specification process which supports independent implementations, or is in the process of being published under such a process.

Normative references

List the normative reference of the media profile:

ISO/IEC 23000-19 Information technology — Coding of audio-visual objects — Part 19: Common media application format (CMAF) for segmented media

W3C Recommendation, TTML Profiles for Internet Media Subtitles and Captions 1.0 (W3C IMSC1), Available at http://www.w3.org/TR/ttml-imsc1

Note: To meet the WAVE Media Profile ‘normative referenceable’ requirement, the organization where the media profile has been or will be published must meet the CTA normative reference policy and be at a level of technical maturity where only editorial changes are possible.

Test and conformance tools

Please provide a timeline for test content and conformance tools.

Test Content

Timeline:

BBC has made available a simple DASH test stream containing CMAF IMSC1 Text format captions using the Blender movie Elephants Dream.

Additional test content may come from the MPEG CMAF conformance process.

W3C IMSC1 tests could also be packaged for detailed testing of IMSC1 features.

Conformance Tools

Timeline:

If MPEG CMAF conformance software is suitable, then the timeline will follow the MPEG timeline for such conformance software.

Note 1: To become an approved WAVE Media Profile the test and conformance tools for content verification as well as test vectors for device verification must be available to WAVE.

Note 2: Media Profiles included in this specification for which no test and conformance material is provided are only published as Provisional WAVE Media Profiles and may be removed if no test and conformance material is provided before releasing a new version of this specification.

For an Approved media profile:

WAVE compatibility

1. Does the media profile specification include its ISOBMFF encapsulation? (Y/N): Y

   1.1. If the case of Y, which organization/spec? ISO/IEC 23000-19

   1.2. In the case of N, ... N/A

2. Have you tested the media profiles with W3C MSE? (Y/N): Y

3. Any reported incompatibilities with W3C MSE? (Y/N): See below

Specification wise, MSE supports this media profile: the MSE spec explicitly allows for the creation of a source buffer providing TextTracks and the media format is packaged in ISO BMFF (as per the CMAF spec) which is included in the MSE Byte Stream registry.

Desktop browsers today don't have support for SourceBuffers containing ISO BMFF packaged IMSC1. Current versions of Chrome, Firefox, Safari and Edge will refuse to add a SourceBuffer for application/mp4;codecs="stpp".