Video Toolkit

Shrink, convert, extract, trim and more — all in your browser via ffmpeg.wasm. Nothing is uploaded. protocol: — build: — accel: —

ℹ️ Browser limitations & quirks (click to expand)

~2 GB memory cap per tab — ffmpeg.wasm is compiled for wasm32, so every pointer is 32-bit. Even on a 64-bit browser/OS the module itself cannot address more than ~4 GB, and most browsers default to 2 GB. This is why 4K HEVC 10-bit clips often fail; use the Memory planner below.
No hardware acceleration for ffmpeg.wasm — the wasm runtime can't access NVENC / Quick Sync / VideoToolbox directly. Encoding runs pure CPU through wasm, typically 10–50× slower than native ffmpeg. However, we automatically fall back to the browser's WebCodecs API (hardware-accelerated) for H.264 / H.265 MP4 sources when supported — the log panel will say “Used WebCodecs hardware path” when this happens.
Memory reporting is browser-specific — Chrome/Edge expose performance.memory; Firefox hides it for fingerprinting. If you're on Firefox, the live “JS heap” field will say “n/a”.
One runtime per tab — after any fatal abort the wasm heap can't be reclaimed. Reload the page between failed attempts.
MT build caveat — the multi-threaded core is ~4× faster but has known quirks with 2-pass encoding and teardown (we work around both).
No GPU filters — everything (scaling, color space conversion, encoding) happens on the CPU.
File size limit — whole input has to fit in memory alongside working buffers. A useful rule of thumb: input file size + output resolution×frames should stay below ~1 GB.

Heads up: This page was opened directly from disk (file://). Chromium-based browsers (Chrome, Edge, Brave) generally cannot spawn the Web Worker that ffmpeg.wasm needs in this context — the loader will hang at “Instantiating WebAssembly”. Serve it via a tiny local server instead:

python -m http.server 8000
# or: npx serve .
# then open http://localhost:8000/video-shrinker.html

1. Choose a video file

2. Operation

3. Options

Target size

Unit

Audio bitrate

Quality mode

Quality (CRF, lower = higher quality)

Audio bitrate

Video codec

Encoder preset

Output container

Audio format

Bitrate (lossy formats)

Start (seconds or HH:MM:SS)

End (seconds or HH:MM:SS, blank = until end)

Trim mode

Columns

Rows

Thumbnail width (px)

Produces a single PNG with evenly-spaced frames.

FPS

Width (px)

Max duration (s)

GIFs are big at any decent quality. Keep width ≤ 480 and duration ≤ 10s.

Threads (MT build only)

Resolution

Scaling behavior Don’t upscale (only scale down)

Presets scale by height and preserve aspect ratio. For custom, leave one field blank to auto-derive it from the other while keeping aspect ratio.

Load core

Read input

Pass 1

Pass 2

Phase

Idle

Elapsed

0.0s

Speed

—

ETA

—

JS heap (current / peak)

—

Heap limit · memory API

—

Load a file to begin.

FFmpeg log