Unlike most online video converters, FreeConvertImg processes your video entirely on your own device using WebAssembly. Nothing is uploaded to a server, so the conversion is completely private and there are no file-size limits imposed by a backend.
The conversion engine (about 30 MB) is downloaded the first time you convert and then cached by your browser, so subsequent conversions start instantly. Larger videos take longer because all the encoding happens locally on your CPU.