Adaptive Bitrate (ABR) in MOQ

How MOQ supports switching between quality levels during streaming.

Overview

moq-msf defines support for adaptive bitrate switching between time-synchronized tracks. Different quality representations are published as separate tracks that share a common timeline.

Mechanism

1. The catalog-format describes all available tracks and their quality parameters
2. Tracks within a renderGroup are time-aligned (though PR #142 clarified this doesn’t imply strict time alignment)
3. Subscribers can switch between tracks by changing their subscription
4. The publish-subscribe model means switching is a client-side decision

Latency Modes

MSF defines three latency regimes that affect ABR behavior:

• Real-time (<500ms) - Minimal buffering, aggressive quality drops
• Interactive (500-2500ms) - Some buffer for smoothing
• Standard (>2500ms) - Traditional ABR with deep buffers

Zapping

PR #122 in the MSF repo adds initial text on “zapping” - quickly switching between different content streams (like changing TV channels). This is related to but distinct from ABR switching.

Related

• moq-msf - Streaming format with ABR support
• catalog-format - Describes available quality tracks
• joining-fetch - ABR implications when joining mid-stream
• media-packaging - Container format affects ABR granularity