Relation of Media to Wall-Clock

[technogeek00]

Use Case Description

Relating of authored media segments to appropriate wall-clock values and signaling of wall-clock values within manifests and playlists.

Working Notes

• Split out of Low latency: DASH target latency and HLS PART-HOLD-BACK are not equivalent #30 as an underlying mechanism requirement
• At the segment level this is the prft mechanism as defined in ISOBMFF
• Relation of tfdt and prft signaling
• There may or may not be appropriate CMAF cross-referencing of this attribute, needs investigation, any CMAF updates needed should be liaison to MPEG
• DASH has explicit signaling to provide the values / relationship in the manifest
• HLS has the program date-time signaling, but does not provide an official relationship / constraint relative to the prft definition
• Express goal of carrying alignment intent, but not a guarantee of synchronization in use-case / scenario description

Open Questions

• What was the previous discussion outcomes around HLS in the low-latency on campus talks?
  • Roger expressed preference to not restrict workflows (reference old notes)
• What is the purpose of specifying latency target interop? Keep DASH and HLS aligned?
  • It's not a guarantee of alignment, i.e. not synchronization
  • It's an opportunity for alignment and carriage of intent to clients

Prioritization Questionaire

Question	Answer
Does the feature relate to an industry streaming use-case?	Live Streaming
- What is the commonality of this case?	Uncommon (but desired)
- Is this an established or emerging practice?	Emerging
Does this feature have related mechanisms in both DASH and HLS?	Sort-of
- What is the maturity of support in both specifications?	DASH - Mature, HLS - Immature
- What is the maturity of implementation support for both specifications?	DASH - Immature, HLS - Immature
- Are there known interoperability issues between specs?	Yes, HLS specification intentionally leaves this underspecified
- Has anyone implemented this interoperably?	Not within manifest/playlist, may have via external means, generally accepted they are not aligned
- 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