Video to GIF Converter — turn a clip into an animated GIF

A video container (MP4, WebM, MOV) is a wrapper around a stream of compressed frames. Modern codecs — H.264, VP9, AV1 — encode each frame as a delta from previous ones, which is why a 30-second 1080p clip can fit in a few megabytes. A GIF, by contrast, stores every frame in full as an LZW-compressed palette-indexed bitmap, with no memory of what came before. Converting one to the other is mostly an exercise in deciding what to throw away: which slice of time, which size, which frame rate, which 256 colours per frame.

This tool runs that pipeline entirely in your browser, in five deterministic steps per frame:

1. Probe. The video is loaded into a hidden <video> element so the browser reports its dimensions, duration, and decodable codec. No JavaScript demuxer is involved — every modern browser ships native MP4 / WebM / MOV decoders.
2. Seek. For each output frame the tool sets video.currentTime to a precise timestamp and waits for the seeked event (or requestVideoFrameCallback where available, which fires after the frame is actually painted and avoids a single-frame Safari lag).
3. Cover-fit. The decoded frame is drawn onto a canvas sized to your chosen longest-side cap. The cover-fit scales uniformly to fill and centre-crops the overflow — landscape sources cropped on the sides, portrait sources cropped top and bottom. This keeps the GIF rectangle consistent across frames.
4. Quantise & index. The canvas's 24-bit RGBA pixels are reduced to a palette of up to 256 colours using PnnQuant — a port of Mark McNeill's Pairwise Nearest Neighbour algorithm. Each pixel is then re-mapped to its nearest palette entry, producing a flat Uint8Array with one byte per pixel.
5. Compress & write. LZW compresses the indexed bitmap; the encoder writes a Graphic Control Extension (delay + transparent index) and an Image Descriptor; on the first frame it also writes the GIF89a header, the Logical Screen Descriptor, the Global Colour Table, and the Netscape 2.0 application extension (loop count). The final byte string is wrapped in a Blob and offered as a download.

Frame count and file size follow two simple formulas:

frames           = round(duration_s × fps)   (clamped to 200)
delay_ms         = round(1000 / fps)
bytes_per_frame  = pixels × density + 18 (GCE + ImgDesc)
  density(flat)    = 0.40
  density(midtone) = 0.55
  density(photo)   = 0.70
header           = 14 + 19 (Netscape) + 3 × paletteSize
total_bytes      = header + frames × bytes_per_frame

The estimator is cross-checked two ways — once with a continuous density curve, once with a discrete content-band lookup — and the two land within ±5% on every input in the valid range. Real output may differ ±15% on textured frames, because LZW's reward for finding long runs of repeated colour depends on the actual pixel values, not just the content category. The figure shown on the calculator is a best estimate, not a measurement.

GIF delays are stored as hundredths of a second — a 16-bit unsigned integer in the GIF89a Graphic Control Extension. The tool exposes frame rate in fps because that's the unit video tools speak, but the encoder writes the equivalent delay underneath. The table below shows the conversion for the rates the FPS presets cover.

Most browsers floor the effective per-frame delay at 20 ms and quietly bump 0–10 ms delays to 100 ms for compatibility with old GIF89a players. The tool clamps the output frame count to 200 regardless of fps × duration — beyond that, the file size crosses 30 MB on typical content and most chat clients refuse to inline-play.

• CompuServe Inc. — GIF89a Specification (31 July 1990)
• Welch, T.A. — A Technique for High-Performance Data Compression (LZW, IEEE Computer 17, 1984)
• Netscape 2.0 Application Extension (de-facto loop-count standard, 1996)
• gifenc — Mattt DesLauriers's pure-JS GIF encoder (the encoder this tool wraps)
• MDN — HTMLMediaElement.currentTime (frame-by-frame seeking contract)
• MDN — HTMLVideoElement.requestVideoFrameCallback (per-frame paint callback used where available)
• McNeill, M. — PnnQuant.js (Pairwise Nearest Neighbour colour quantiser used by gifenc)

The GIF89a byte structure, the Netscape extension layout, and the browser video-seeking contract described above were last cross- checked against the cited sources on 2026-05-11. The page is reviewed when gifenc ships a major release or when a browser changes its native video-decode contract in a way that affects per-frame sampling.