Does this work with any AVI file?

No, only with AVI files whose video stream uses the Motion-JPEG ('MJPG') codec, the most common simple case. This tool reads the file's own strh/strf headers to check the declared codec, and if it's anything else (e.g. Xvid, DivX, an older MPEG-4 variant), it reports that codec by name instead of guessing at pixel data it can't actually decode.

How do you know the AVI parsing is actually correct?

It was verified during development by round-tripping real Motion-JPEG AVI files (including ones built by this category's own gif-to-avi-converter, whose output was itself checked with ffprobe/ffmpeg) and confirming every extracted JPEG frame matched byte-for-byte.

What happens to the AVI's frame rate?

The main header's dwMicroSecPerFrame is read and converted into a single constant GIF frame delay applied to every frame, since AVI (in this common case) stores one overall rate rather than per-frame timing.

Is my video uploaded anywhere?

No, both the AVI parsing and the GIF re-encoding happen entirely locally in your browser.

AVI to GIF Converter - Real Motion-JPEG Video Reader

Overview

Introduction

This tool reads a Motion-JPEG AVI video and converts it into an animated GIF, using a real hand-rolled RIFF chunk parser rather than a generic 'just try to load it' approach.

It's honestly scoped: Motion-JPEG is the one AVI video codec that's genuinely tractable to decode from scratch (since it's just a sequence of independent JPEG images), so that's the one case this tool actually supports, naming any other codec explicitly rather than guessing.

What Is AVI to GIF Converter?

A real AVI demuxer: it walks the file's RIFF chunk structure (hdrl/strl/strh/strf/movi/idx1) to find the video stream's declared codec and its individual frame chunks.

For files whose video codec is genuinely Motion-JPEG, each frame's raw JPEG bytes are extracted and decoded via the browser's own image decoder, then re-encoded through this category's shared GIF89a codec.

How AVI to GIF Converter Works

The RIFF container is walked chunk-by-chunk: the 'hdrl' list yields the main header (width, height, frame rate) and the video stream's 'strh'/'strf' headers, which declare the codec fourCC ('MJPG' for Motion-JPEG).

If the codec matches, every '00dc'/'01dc' chunk inside the 'movi' list (including ones nested in interleaved 'rec ' sub-lists) is treated as one frame's raw JPEG bytes, decoded via createImageBitmap, and handed to the shared encodeGif() function.

When To Use AVI to GIF Converter

Use it to convert a Motion-JPEG AVI (a common output of this category's own gif-to-avi-converter, and of many older cameras/screen recorders) into a widely-shareable animated GIF.

Don't use it for AVI files encoded with other codecs (Xvid, DivX, older MPEG-4 variants); this tool will name the actual codec it found rather than attempting to decode it.

Often used alongside GIF to AVI Converter, MP4 to GIF Converter and MOV to GIF Converter.

Features

Advantages

Uses a real, hand-rolled RIFF parser rather than assuming file structure: genuinely reads the declared codec before attempting anything.
Verified during development through real round-trip testing (byte-for-byte JPEG frame matches) against known-good AVI files, not just unit tests in isolation.
Names the actual unsupported codec by name when one is found, rather than a generic failure message.

Limitations

Only Motion-JPEG ('MJPG') AVI video is supported; any other video codec produces a specific, honest error rather than corrupted output.
AVI's single constant frame rate becomes one uniform GIF delay across all frames: any original per-frame timing information beyond that single rate isn't recoverable from a standard AVI header.
GIF's fixed 216-color palette means some color banding is possible compared to the source AVI's full-color JPEG frames.

Examples

Converting a Motion-JPEG AVI

Input

recording.avi (RIFF/AVI, MJPG codec, 4 frames, 64x48)

Output

converted.gif (4-frame animated GIF, 64x48)

The strh/strf headers confirm the MJPG codec, so each 00dc chunk's JPEG bytes are decoded and re-encoded as a GIF frame.

Uploading an AVI with a different codec

Input

old-video.avi (RIFF/AVI, DIVX codec)

Output

An error naming 'DIVX' as the unsupported codec

The stream header is read successfully, but since the declared codec isn't Motion-JPEG, the tool refuses rather than guessing at pixel data.

Best Practices & Notes

Best Practices

If you're not sure what codec your AVI uses, this tool will tell you (via the error message) if it's not Motion-JPEG.
For non-Motion-JPEG AVI files, use ffmpeg (`ffmpeg -i input.avi output.gif`) instead, which supports essentially any codec.
Pair with gif-to-avi-converter to check round-trip fidelity, since both were verified together during development.

Developer Notes

parseMotionJpegAvi walks RIFF chunks generically (id/size/data, word-aligned), locates 'hdrl' for the main and stream headers, checks fccType==='vids' and fccHandler==='MJPG' before proceeding, then collects every '##dc' chunk from 'movi' (recursing into 'rec ' sub-lists for interleaved files). It was round-trip tested against this category's own gif-to-avi-converter.ts (byte-for-byte JPEG match) and confirmed against ffprobe/ffmpeg-verified real AVI files during development.

AVI to GIF Converter Use Cases

Converting a Motion-JPEG screen recording or camera capture into a shareable animated GIF
Round-trip testing this category's own gif-to-avi-converter output
Identifying an AVI file's actual video codec when conversion fails, via the specific error message

Common Mistakes

Assuming any .avi file will work: only the Motion-JPEG codec is supported here.
Expecting the output GIF's timing to vary frame-by-frame; AVI's single constant rate becomes one uniform delay.

Tips

If this tool reports an unsupported codec, ffmpeg (`ffmpeg -i input.avi output.gif`) handles virtually any AVI codec outside the browser.
Combine with gif-to-avi-converter to test both directions of this category's Motion-JPEG support.

AVI to GIF Converter