Burn subtitles into 4K video — free, in browser
Most subtitle tools downscale 4K to 1080p on the free tier. BurnSub processes 4K natively and exports 4K. No upload. WebCodecs + WebGPU running on your hardware.
4K support comparison
| Feature | BurnSub | Veed.io | Kapwing | Clideo |
|---|---|---|---|---|
| 4K input on free tier | ✓ | ✗ (Pro) | ✗ (Pro) | ✗ (Pro) |
| 1080p input | ✓ | ✓ | ✓ | ✓ |
| Output resolution | Same as input | Down-scaled | Down-scaled | Down-scaled |
| H.265 / HEVC support | ✓ | Limited | Limited | Limited |
| Vertical 4K (TikTok-style) | ✓ | ✓ | ✓ | ✓ |
| GPU acceleration | Local WebGPU | Cloud | Cloud | Cloud |
What "4K supported" actually means
Most cloud editors say they "support" 4K — but on the free tier they downscale your output to 1080p, watermark it, and gate full-quality 4K behind Pro. BurnSub doesn't downscale. The output is the same resolution and bitrate as your input.
Why this works in the browser
WebCodecs gives the browser direct access to the GPU's H.264 / H.265 decoder — the same hardware that plays YouTube 4K. When you drop a 4K file, your GPU decodes frames at near-native speed. Whisper-Turbo transcribes audio on the same GPU via WebGPU compute shaders.
Encoding back to 4K H.264 is the slowest step. On an M1/M2 Mac or recent Intel/AMD laptop with hardware encode, expect ~1× realtime (a 5-minute 4K clip takes ~5 minutes to encode). Older devices may take longer.
What 4K formats are supported?
- 3840×2160 (UHD) — H.264 and H.265 / HEVC, MP4 and MOV containers.
- 4096×2160 (DCI) — works for cinema-spec footage.
- 4K vertical (2160×3840) — TikTok / Reels-shaped 4K, fully supported.
- 4K60 — supported as long as your hardware can decode 60 fps.
Will BurnSub work on a phone in 4K?
Modern iPhones (15 Pro+) and Samsung flagships handle 4K decode well in Safari/Chrome. Older phones may stutter or run out of RAM on long clips. For long 4K projects, a laptop is faster.
Why is 4K free here but Pro elsewhere?
Cloud tools pay GPU time for every uploaded video. 4K processing costs them 4× as much as 1080p, so they paywall it. BurnSub uses your GPU, not theirs — there's no cost to recoup, no Pro tier to gate.