haudiobe
commented
10 years ago ANSI/SCTE 128 2010-a as available here http://www.scte.org/documents/pdf/Standards/ANSI_SCTE%20128%202010-a.pdf defines in section 8.1 some bits and pieces. Please read it.
Based on this it means that the details that the video track carries SEI message that carry CEA-608/708 CC is accessible only very deep down in the hierarchy as the SEI message payload_type=4 is used that indicates that Rec. ITU-T T.35 based SEI messages are used. In summary the following is included in ANSI/SCTE 128 2010: SEI payloadType is set to 4 itu_t_t35_country_code – A fixed 8-bit field, the value of which shall be 0xB5. itu_t_35_provider_code – A fixed 16-bit field registered by the ATSC. The value shall be 0x0031. user_identifier – This is a 32 bit code that indicates the contents of the user_structure() and is 0x47413934 (“GA94”). user_structure() – This is a variable length data structure ATSC1_data() defined in section 8.2 user_data_type_code is set to 0x03 for indicating captioning data in the user_data_type_structure() user_data_type_structure() is defined in section 8.2.2 of ANSI/SCTE 128 2010 for Closed Captioning and defines the details on how to encapsulate the captioning data. We discussed with MPEG File Format and DASH experts on how to provide the signalling of the presence of the data on MPD level. There was not really a great solution proposed for this, but we could agree on a temporary fix using the profile/brands parameter in the file format.
The temporary proposal is the following. An ISO BMFF file may carry a compatibility brand “c708". If the ISO BMFF file carries an c708 brand then it shall include exactly what is defined above: SEI payloadType 4 and all the details up there. The profiles of the brand can be signalled in the MIME Type and therefore can be included in the MPD. We should mandate the inclusion of the parameter if present. We should also add appropriate Accessbility/Role parameters to the video Representation if the SEI is present We share the problem and the temporary solution with MPEG and ask for guidance of they believe we should use this approach or if they have a different proposal.
As we have closed captioning with DASH-264/AVC, we want to add this interoperability point to DASH-264/AVC. In addition an MPEG contribution should be submitted to enable the signalling of SEI messages that are present in the video track.