Adaptive bitratePRO
How adaptive bitrate works and when to enable it.
Overview
Adaptive bitrate (ABR) dynamically adjusts encoder output to available network capacity across active connections. It reduces risk of interruptions versus fixed bitrate when conditions fluctuate.
Key Points
- Only one stream can use adaptive bitrate at a time.
- Supported with transport methods: TCP and Bifrost.
- Immediate reaction to capacity drops; ramp-up is conservative to avoid oscillations.
When to Use
| Situation | ABR Value |
|---|---|
| Mobile / cellular bonding with variable throughput | Essential |
| Fixed fiber / guaranteed bandwidth | Optional (fixed CBR fine) |
| Critical low-latency interview (strict latency target) | Consider fixed tuned bitrate |
| Long-form events with unpredictable crowd network load | Recommended |
Interaction with FEC / Retransmission
- Bifrost ABR balances sending rate with loss recovery overhead.
- Adding FEC to RTP does not equate to ABR—FEC is static redundancy, ABR is dynamic source bitrate control.
Operational Tips
- Set a sensible max bitrate ceiling matching encoder profile capabilities and receiver decoding headroom.
- Monitor ISS graphs after enabling—look for stable average near target with brief dips (healthy) versus sawtooth spikes (indicates contention or overshoot).
Troubleshooting
| Symptom | Possible Cause | Action |
|---|---|---|
| Frequent bitrate floor clamps | Chronic low network capacity | Lower max, consider higher compression (HEVC) |
| Oscillation / instability | Competing traffic shaping | Reserve QoS or cap competing flows |
| Receiver buffer underruns | Latency too aggressively minimized | Increase buffer, allow ABR more margin |