Video Converter

A video converter changes the format of a video file. Most of the time that means changing the container, the wrapper that holds the picture and sound streams and tells a player how to find them. MP4, MOV, WebM and AVI are containers. H.264, VP9 and AAC are codecs, which is the actual compression inside.

The distinction matters because it decides whether a conversion costs you anything. A MOV recorded by an iPhone, a Mac screen recorder or most cameras already holds H.264 video and AAC audio, and that is exactly what an MP4 holds. Going from one to the other is a remux: the streams are copied into a new wrapper without being decoded. It takes seconds, and it is lossless, because no pixel is re-examined. A converter that re-encodes for this job spends minutes throwing away quality to produce a file that could have been identical. This tool copies by default and only re-encodes when the formats genuinely require it.

Converting to GIF is the opposite case and the one where quality is usually lost badly. A GIF holds at most 256 colours for the whole image, so every conversion has to pick which 256. Done frame by frame, which is what a plain conversion does, the same shirt ends up a slightly different colour in consecutive frames and the picture appears to crawl. The fix is two passes: look at the entire clip, build one palette for all of it, then encode against that palette. This tool runs both passes. It is also why a GIF of anything long is enormous, since GIF stores whole frames rather than the differences between them, and a few seconds at a reasonable size will often be larger than the video it came from.

The other direction, GIF to MP4, is almost always worth doing. The same animation as H.264 is typically a tenth of the size and plays on anything, which is why social platforms quietly convert every GIF you upload. The one catch is that H.264 refuses odd pixel dimensions, and GIFs frequently have them, so the conversion has to round the size down to an even number or it fails outright.

Everything runs inside the browser through ffmpeg compiled to WebAssembly. The file is read from your disk into the page, converted in the tab, and handed back as a download. No server receives it, nothing is queued, and there is no copy to delete afterwards because none is made. You can check in devtools: no request carries the video. It also means the limits here are your browser tab’s memory rather than an upload quota.