Lower Latency, Startup and Switching for DASH (L3D)

1. Lower Latency, Startup and Switching for DASH (L3D)

1.1. Introduction

This feature description is an update to DASH-IF Low-Latency extensions [IOP5-PART4-LL] adding additional features.

1.2. Scenarios and Motivation

In 2017, DVB (https://www.dvb.org) and DASH-IF (https://www.dashif.org) started to collaborate to address Low-Latency DASH-based services. Initially, a joint group was formed that developed a report that was issued by DVB/DASH-IF as _DASH-IF/DVB Report on Low-Latency Live Service with DASH_ [LL-REPORT].

Based on this report, the DASH-IF Low-Latency extensions [IOP5-PART4-LL] were developed and published, together with test streams and dash.js implementation.

Add the references to dash.js

provide a summary of what could be achieved

• Reviewing the Report - what has changed

  • Do have new requirements in terms of latency < 3 seconds?

    • There are new requirements that sports events may needed less than 3 seconds, but not that hard

    • We have the report here: https://dashif.org/webRTC/report

      • Betting use case may be of relevance.

      • Please check if any of the use case matter as is or in variants for the work we are planning top

  • Do we have new requirements to tune and switching?

    • faster tune-in, time to first video is very important and should be low (1-2 seconds may be too high)

    • Start playback faster – do not wait for up to 2 seconds

    • Faster switching to avoid buffering

    • Independency of joining latency, switching latency and segment duration

  • Do we have new requirements for efficiency?

    • _Compression efficiency_

    • _Enables scene-boundary aligned segments_

    • _Mini-GOP-sized partial segments for random access and events_

  • Are there any new use cases that requires new technology?

    • Ad insertion w/o stream conditioning

      • Return from ad break to an arbitrary place – not necessarily an IDR

    • LL-HLS compatibility

      • Reuse LL-HLS partial segments

      • Use DASH templates to keep same MPD update efficiency

    • Trick modes

      • Small partial segments can be used for smoother trick play

  • Did the defined technology for LL-DASH not meet the requirements?

    • The technology may meet the requirements in terms of latency, but at the expense of reduced quality, including more re-buffering and/or reduced compression efficiency

    • Today’s technology typically requires that segment durations are in the range of 2 seconds.

• Next Steps

  • add the above logic to the introduction of the feature.

  • Start documenting the technology by reference to 6th edition

  • also document client requirements

1.3. Content Offering Requirements and Recommendations

1.4. Client Implementation Requirements and Guidelines

1.5. Examples

NOTE: Add some MPD examples

1.6. Reference Tools

NOTE: provide status for the following functionalities

• Dash.js

• Live Sim

• Test Vectors

• JCCP

1.7. Additional Information