There are two definitions of video streaming. True video streaming is when the server maintains a connection with the client and the client is intelligent enough to pass data back to the server telling it things like, (1) need more data, (2) pause - stop sending data, or (3) skip ahead to 2 hours, 10 minutes into the video. The advantage of True Video Streaming is that when the client doesn't want to see the first 2 hours and 9 minutes of the video, you don't waste the bandwidth downloading gigabytes of data that he's just going to skip. This also means that when the client wants to skip ahead, he can skip to the end almost instantly.
Progressive downloads feel a little like streaming because they can start playing in the client's video player even before the entire video has been downloaded but, since it's not true streaming, when he tries to skip ahead to 2 hours and 10 minutes, he has to wait for a long time (maybe an hour or two) before the video has entirely loaded before he can start seeing that part of the video.
And then the third type of video is just dumping a MPEG / AVI / WMV type file onto your web site. This is delivered by the web server instead of a special video streaming server. This video won't even start to play until the entire video is downloaded. (For this reason, anything bigger than about 9 MB is discouraged).
No matter which of those three types of video you choose to use, the delivery of the video has nothing to do with PHP. You will need a web page - it doesn't matter whether the web page was written in PHP or simple HTML. (Or anything else for that matter). And if you're using streaming, then you'll need to install a video streaming server which is beyond the scope of these forums because it's not streaming from PHP.
