As which patent free format can be used, for audio the format ogg vorbis is well known and works on all platform, unfortunately on windows you need to download plugins.

For Video the format is oog Theora, which is still in beta but works, and there the plugins are even more rare.

However it is not uncommon to use several formats when streaming to cater for the difference of bandwidth of the clients but as explained you need to have a clue of what you are doing because then you need specialised streaming software.

Now if you don’t need to stream, the most common platform in use is flash, it works everywhere, however you cannot download the file to play later.

There is still some work to be done on streaming, but raising awareness, get people thinking. It is like asking your upstream provider for an IPv6 address, it won’t happen till a lot of people ask.