There are literally thousands of wrappers for ffmpeg (other examples: imagemagick, ghostscript) that do exactly that. E.g. all commercial and dozens of open source video converters. So there is no lack of simple software for people who know little about the problem they're trying to solve (e.g. playing a downloaded mkv their shitty preinstalled video player doesn't accept), the problem is rather one of knowing that open source software exists and how to find it. Googling or asking an LLM does mostly present you software that costs money and is inferior to anything open source (and some malware).