"My line does 100 Mbps, why does 4K still stutter?" — usually the answer is not bandwidth. Let us get the numbers straight first.
Bandwidth by resolution
| Resolution | Typical bitrate | Stable bandwidth needed | Per hour |
|---|---|---|---|
| 480p | 1–2 Mbps | 3 Mbps | ~0.5 GB |
| 720p | 3–5 Mbps | 6 Mbps | ~1.5 GB |
| 1080p | 5–8 Mbps | 10 Mbps | ~2.5 GB |
| 1440p | 10–16 Mbps | 20 Mbps | ~5 GB |
| 4K (2160p) | 15–25 Mbps | 30 Mbps | ~7 GB |
| 4K HDR / high frame rate | 25–40 Mbps | 50 Mbps | ~12 GB |
So 4K needs surprisingly little: a stable 30 Mbps suffices. A 100 Mbps line could in theory carry three simultaneous 4K streams.
So why does it still stutter?
Jitter is the leading cause. A relayed route at peak hours does not go uniformly slow; it goes up and down. A speed test reads 80 Mbps, but during playback it dips to 5 Mbps every fifteen seconds, the buffer drains and the video stalls.
Telling them apart
| Symptom | Likely cause | How to check |
|---|---|---|
| Slow to start, then fine | High latency | Look at the real-delay figure |
| Repeated brief stalls | Jitter or packet loss | Run the speed test three times and compare |
| Always drops to 720p automatically | Sustained bandwidth shortfall | Run a dedicated download test |
| Video stutters but audio is fine | Decoding performance | Try a lower resolution or another device |
| Only one site is affected | CDN routing for that service | Try a server in another region |
What actually helps
- Change server region. Streaming CDNs differ; a Japanese server may be smooth where a Hong Kong one stalls.
- Prefer dedicated lines. IEPL/IPLC routes have markedly lower jitter at peak — precisely what you pay for.
- Lock the resolution manually. Automatic quality switching thrashes on a fluctuating line and feels worse than a fixed lower setting.
- Close bandwidth-hungry background tasks. Cloud sync, system updates and downloads compete for the same pipe.
- Prefer wired over wireless. The 2.4 GHz band jitters badly in crowded environments; move to 5 GHz or plug in.
A one-minute test
No tools required: open a 4K video, force the quality to 4K, and watch for three minutes.
- No stalls in three minutes → this route handles 4K.
- One or two brief stalls → jitter is high; 1080p will be far more comfortable.
- Frequent stalls or automatic downgrades → change server, or accept a lower resolution.
This beats any benchmark number, because it measures exactly the thing you care about.