Video FPS
Understand video frame rate measurement in VoIP calls — how CallMeter tracks FPS, what frame rate drops mean for visual quality, and common causes of choppy video.
Video FPS (Frames Per Second) measures the rate at which video frames are produced or rendered. Higher frame rates produce smoother motion. Lower frame rates make the video appear choppy and stuttering. For video calls, 30 fps is the standard target, while screen sharing often uses 15 fps or lower.
Think of it as the smoothness of a flipbook animation. Thirty pages per second creates fluid motion. Fifteen pages per second is acceptable but visibly less smooth. Below 10 pages per second, the animation becomes noticeably jumpy.
How It Works
The video encoder produces frames at a rate determined by its configuration, the video source, and current conditions. CallMeter measures the actual frame rate by counting decoded video frames per second.
Typical frame rate targets:
| Use Case | Target FPS | Notes |
|---|---|---|
| Video call (camera) | 30 fps | Standard for face-to-face communication |
| Screen sharing | 10 - 15 fps | Motion is rare; lower FPS saves bandwidth |
| High-motion video | 30 - 60 fps | Sports, demos, or live events |
Both directions
FPS is measured separately for send and receive. Send FPS reflects the encoder's output rate. Receive FPS reflects what the decoder actually renders, which may be lower if packets are lost or arrive late.
Why It Matters
Frame rate directly impacts the viewer's perception of video quality:
- 30 fps — Smooth motion, natural-looking video for calls
- 15 - 20 fps — Noticeable but acceptable; typical during bandwidth pressure
- Below 10 fps — Obviously choppy; motion appears as a slideshow
- Below 5 fps — Nearly unusable for real-time communication
For enterprise testing, FPS drops are a key quality indicator. They often appear before more severe problems like freezes, making them a useful early warning signal.
Common Causes of Low FPS
| Cause | Explanation |
|---|---|
| Bandwidth congestion | Encoder reducing frame rate to fit within available bandwidth |
| CPU overload | Encoder cannot process frames fast enough |
| Resolution too high | Encoding high resolution consumes CPU, forcing FPS reduction |
| Packet loss on receive | Decoder missing frames due to lost packets, reducing effective FPS |
| Video source limitation | Camera or capture device limited to a lower frame rate |
How to Fix It
- Check bitrate alongside FPS — If Video Bitrate drops at the same time as FPS, congestion is likely the cause. Address bandwidth.
- Monitor encoder CPU — If the sending device is CPU-constrained, reduce the encoding Resolution to free up processing headroom for maintaining FPS.
- Compare send vs receive FPS — If send FPS is 30 but receive FPS is 15, packets are being lost in transit. Focus on network quality.
- Review encoder settings — Ensure the encoder is configured to prioritize frame rate over resolution when bandwidth is limited (prefer smoother video over sharper but choppy).
- Reduce resolution first — When bandwidth is tight, reducing resolution while maintaining 30 fps usually provides a better experience than maintaining resolution at 15 fps.
Related Metrics
- Video Bitrate — Bitrate and FPS are closely linked; both drop during congestion
- Resolution — Resolution may decrease to maintain FPS under pressure
- Video Freeze Events — FPS drops to zero during a freeze event
- Video Freeze Duration — Extended zero-FPS periods measured as freeze duration
- Packet Loss Rate — Receive-side FPS drops when packets are lost
Video Bitrate
Understand video bitrate measurement in VoIP calls — how CallMeter tracks encoding bitrate, what bitrate changes reveal about network adaptation, and how to interpret bitrate trends.
Resolution
Understand video resolution measurement in VoIP calls — how CallMeter tracks resolution in megapixels, what resolution changes reveal about quality adaptation, and common causes of resolution drops.