There are number ways to add support of Video uploading, converting and playing facility using php.
Uploading be achieved using Jquery Uploadify plugin. Its really nice. but make sure that you have set the PHP max UPload size and file size, you might also increase your script execution time if you are dealing with heavy files.

Simpliest way fir conversion is   ffmpeg. and run it using php exec function. if you want to generate the tumbnail from the video. it can also be achieved by ffmpeg by providing it certain parameters to extract the frame from vidio. and than you can resize it or save it using imagemagk.

JW palyer can be used to play video online using its live stream functionality.

There is PHP media parser GetID3(). The PHP media file parser extracts play time, bitrate and resolution from AAC and reads/writes ID3v1/v2 tags, supports other formats as well.

Vidiscript is another Video open source component which can be used. it is very detailed package and can provide almost all youtube functionalities. Its worth exploring it. But not all hosting provider support all the prequisits required for this.

http://vidiscript.com/index.html