How AVI conversion works here
AVI (Audio Video Interleave) is Microsoft's container from 1992. No mainstream browser plays it, so the page loads ffmpeg.wasm, a WebAssembly build of FFmpeg, the first time you open an AVI. FFmpeg reads the old codecs inside (DivX, Xvid, MJPEG, Cinepak, H.264) and makes an editable H.264 copy of the first 60 seconds, scaled to at most 720 px wide, in your browser's memory. From there the trimming, cropping and GIF encoding are the same as for any other file.
- First run: about 32 MB to download, then cached by your browser.
- Speed: single-threaded WebAssembly is several times slower than desktop FFmpeg. A one-minute 480p AVI typically takes 20 to 60 seconds on a laptop.
- Size: the whole file is read into memory, so very large AVIs (many hundreds of MB) can fail on phones. Trim long recordings on a computer first.
Want the GIF from later in a long AVI? The converter takes the first 60 seconds, so cut the part you need first in any video editor, or convert the AVI to MP4 with a desktop tool and load that.
Good settings for old AVI footage
Old AVIs are often 320×240 or 640×480 with visible compression blocks. Keep the GIF width at or below the source width (upscaling only enlarges the file), use 10 to 12 fps, and try Ordered dithering, which hides blockiness better than none.
Questions
Why does AVI take longer than MP4?
Browsers cannot decode AVI, so ffmpeg.wasm has to convert it first, on your device, using WebAssembly, which is slower than native code.
Is my AVI uploaded to a server for conversion?
No. ffmpeg.wasm runs inside your browser tab. The only download is the FFmpeg program itself, from this site.
Can I convert only part of a long AVI?
The ffmpeg.wasm route converts the first 60 seconds. For a clip further in, trim the AVI in a desktop editor first.