Keyframe Requests Sent
Understand outbound keyframe requests in video streams — what they measure, why a high count signals video corruption, and how to reduce keyframe request frequency.
Keyframe Requests Sent counts the number of keyframe requests your endpoint has sent to the remote side during a video call. Each request is a signal that the local video decoder has lost synchronization and needs a complete picture (keyframe) to recover.
Think of it like asking someone to start their story over because you missed a critical part. Once or twice is normal. Asking repeatedly means you keep losing the thread — and in video terms, that means the picture is breaking down.
How It Works
Video codecs compress data by encoding most frames as differences from the previous frame (delta frames or P-frames). This works well until a packet is lost — without the reference data, subsequent frames cannot be decoded correctly, causing visual corruption.
When the decoder detects this corruption, it sends a keyframe request back to the sender via RTCP feedback. Two common request types exist:
- PLI (Picture Loss Indication) — A polite request: "I lost some data, please send a keyframe when convenient"
- FIR (Full Intra Request) — An urgent demand: "My decoder state is completely broken, send a keyframe immediately"
CallMeter counts all outbound keyframe requests (both PLI and FIR) and reports them per measurement interval.
Why It Matters
Every keyframe request represents a moment where the video viewer saw corruption, artifacts, or a frozen image. The video does not recover until the keyframe arrives and is successfully decoded — which can take hundreds of milliseconds.
For enterprise VoIP testing, the keyframe request rate is a leading indicator of video quality problems:
- Sparse requests — Normal operation, occasional packet loss recovered quickly
- Frequent requests — Persistent video corruption, poor viewer experience
- Escalating requests — Worsening network conditions or a systematic problem
Common Causes of High Keyframe Request Counts
| Cause | Explanation |
|---|---|
| Network packet loss | Lost video packets break the decoder's reference chain |
| Insufficient bandwidth | Video bitrate exceeds available capacity, causing drops |
| Jitter buffer overflow | Late packets discarded, creating gaps in the video stream |
| Firewall or NAT issues | UDP packets dropped by stateful network devices |
| Encoder errors | Sender producing malformed video data |
How to Fix It
- Check packet loss — Review Packet Loss Rate to confirm whether network-level loss is driving the keyframe requests.
- Verify bandwidth — Compare Video Bitrate against available network capacity. If the bitrate is close to the link capacity, congestion drops are likely.
- Enable NACK retransmission — NACK messages allow the receiver to request retransmission of specific lost packets, often recovering the video without needing a full keyframe.
- Review QoS configuration — Ensure video RTP packets are marked with appropriate DSCP values for priority handling.
- Reduce video resolution or framerate — Lower Resolution or FPS to reduce bandwidth demand and packet loss probability.
Related Metrics
- Keyframe Requests Received — Requests the remote side is sending to your endpoint
- Keyframes Sent — How many keyframes were actually produced in response to requests
- Keyframe Interval — Time between keyframes, affected by request frequency
- Video Freeze Events — Freezes often trigger or result from keyframe requests
- NACK Messages — First-line packet recovery before escalating to keyframe requests
RFC Reference
PLI (Picture Loss Indication) is defined in RFC 4585 (Extended RTP Profile for RTCP-Based Feedback), Section 6.3.1. FIR (Full Intra Request) is defined in RFC 5104 (Codec Control Messages in the RTP Audio-Visual Profile with Feedback), Section 3.5.1.
Audio Level RMS
Understand overall audio RMS level measurement — how CallMeter tracks the volume of the complete audio signal, thresholds for detecting silence and clipping, and why it matters for call quality.
Keyframe Requests Received
Understand inbound keyframe requests — what they measure, why the remote side is requesting keyframes from your endpoint, and what it means for overall video quality.