Carriage of In-Band Events

[technogeek00]

Use Case Description

Carriage of media timed events to end players through the authored media segments.

Working Notes

• Previously in Carriage of Manifest Events #35 but in-band and manifest split to separate tickets.
• Events can be a combined subsection in 4 and 5 but we will consider topics separately.

Open Questions

• Are there any conflicting statements on in-band event support between specifications?
• Can an HLS client operate on the DASH-IF Event timing model?
• Note HLS implicit allowance, no explicit signal in playlists

Prioritization Questionaire

Question	Answer
Does the feature relate to an industry streaming use-case?	Yes, Timed Metadata Events
- What is the commonality of this case?	Uncommon (outside of SCTE35)
- Is this an established or emerging practice?	Emerging
Does this feature have related mechanisms in both DASH and HLS?	Yes
- What is the maturity of support in both specifications?	DASH - Mature, HLS - Mature
- What is the maturity of implementation support for both specifications?	DASH - Mature, HLS - Mature
- Are there known interoperability issues between specs?	Potentially, lack of definition in HLS
- Has anyone implemented this interoperably?	Yes
- Are there features missing in a specification with open proposals for it?	No
Has the industry defined defacto mechanisms not present in both DASH and/or HLS?	No
- Why was functionality defined outside of the main specifications?	N/A
- Has the functionality been standardized elsewhere (DASH-IF, CTA, SVA)?	N/A
- Is the functionality proprietary or openly developed?	N/A
- Could the functionality be incorporated into specifications with evangelism?	N/A

[technogeek00]

From @nicoweilelemental on #35

In-Band Timed Metadata Events Based
The ID3/CMAF spec (https://aomediacodec.github.io/id3-emsg/) is in the AOM realm, not the HLS or DASH one. That would be great to integrate it into the core CMAF spec at MPEG, as this is a foundational mechanism.
The other main point of attention I see is the HLS playlist signaling: while we can tell the player which type of inband events is included in a given track, it's not possible in HLS. The common use cases we see in CMAF-based deployments are ID3 and KLV. Inband SCTE35 signaling, although implemented, is not a very popular feature as most of the ad insertion happens on the server side. Outside of ad insertion use cases, it's unlikely that other SCTE35 features like content chaptering would be implemented through inband signaling, as players need to get the information when a program is loaded initially, not during the playback session when loading a segment.

[technogeek00]

General Notes (05/04/2022)

• emsg mechanism generalized for carriage in CMAF, recommend for interop
  • Legacy HLS ID3 bindings given emsg binding in AOM spec
• DASH has official signaling support with InbandEventStream element
• HLS has no official signaling with no open proposals
• W3C Media timed events document has some nice detail summaries as well, but is primarily focused on player functionality and not signaling