There are 3 ways to create a streaming site:
1) Affordable: Upload apple format movies to your server and link them to your page. This is basically playing movies from your server. yet Apple is a dominate plugin that many users have.
2)Utilizing you tube server and embedding video to your site. Affordable but information privacy is at risk.
3) Purchasing Flash server program to stream flash media to your site and allow it to be streamed to others. It is what YouTube uses and many other popular sites.
4) There is a flash alternative that allows for users to share a flash server system, but this is a recent development I have heard of so you might want to research it to see what is possible.
What you must consider is the plugins. Its similar to browser wars. flash is the dominate type because it is free to use by the users, no other plugin actually exist except for apple and windows players. Ubuntu has VLC(which is a great player) but it doesn't have a plugin.
And I assume flash is the only browser type plugin to(plays totally from the browser). Others I know of actually use the systems software to play through the browser.
As far as developer specific I think application varies. depending on playing from system, to a full feature youtube, dailymotion, etc. type system which have to have flash server.
But in short flash server should be your first stop to see if you need that type of application and just work back if not.
Remember PHP can help with server data generation(your movies), so server-side application may play a big part too, as far as displaying info to a page.