Most common formats that don't require any software or CODEC installs I have a small MP4 file that I need to send to someone on a USB stick. Without knowing anything about the PCs that this person has access to, how can I be reasonably certain he will be able to play it without needing to install any software or codecs?

Should I just convert the video to several different formats? What are the most common ones that require the least hassle? (I wouldn't be surprised if something as old as Windows XP is used in this case)
I've always used H.264 and have never had any issues with anyone being able to view it on Windows or Mac. H.264 is my standard go-to for formats, but as you mentioned, it might not hurt to convert it to several different codecs/formats, especially if it is a small file.