The video will most likely open with Windows Media Player. All PCs running any version of Windows come with this built in video player. Windows 11 and under will not open MP4 file without a codec or third party decoder. [1] X Trustworthy Source Microsoft Support Technical support and product information from Microsoft. Go to source
It’s always recommended to use the bundled media playback software that ships along with your operating system; but, because they ship free with your operating system, they may not quite effectively play all the file formats. There are both free and paid software available. Some free softwares like VLC Media Player, Media Player Classic, etc. are some of the best and most widely used softwares. They support playback of nearly all the video and audio file formats.
