What is the best universal video format / extension so that it can be viewed on iPad and PCs So, someone asked me this question today, and I am very curious about the answer. This person wants to put up a video on a website, and wants it to be viewable on both the iPad and on PCs. They don't mind providing two links, but they seemed to lean slightly more to the idea of having one link. Plus, I am very curious to the answer.

Also, they were telling me how when they go to YouTube to view a video, they can view it regardless of accessing the video from their iPad or a computer. I told them that this is because YouTube has multiple versions / formats of a video and shows you the format best suitable for your device. Was that answer correct? And being that one video on YouTube can be accessed / viewed regardless of device, I am not sure if this person has any kind of opposition to posting the video on YouTube.

Assuming they do though, I have these questions:

1) If I were to put a direct link to a video on a website for people to view (using whatever default player is available on their device to play videos) or download, and I want that one video to be viewable regardless of the device accessing it, what's the best video format / extension to use--flv, mp4, etc.?

2) If I wanted to go a step further and use my own embedded video player, what's the best one to use, best in the sense that it can be viewed on as many platforms as possible, especially the iPad and personal computers? I see the jw player used on lots of sites. I don't have an iPad though, so I can't test it.
h.264 is very widely supported and can be found in multiple different types of container formats.  mp4 or m4v are probably the most widely used extensions, but particular support for files varies based on what players are installed on devices.

MP4 is the official MPEG 4 standard container format.  M4V is an originally Apple based container which also added AVC support, but is still a bit more open than MOV.  Most players will also interchangeably play a file regardless of an M4V or MP4 extension provided that they support reading both file formats.

MP4 probably has slightly better overall compatibility while M4V probably has slightly better compatibility on Apple devices, but that is also subject to change and is hard to measure accurately.