Hello!
Video player is not very easy task. Different browsers work with video in different manner. File size does matter for player; web-server should process some special queries.
So please let’s prepare more detailed description of the job.
What is the video source? File on web-server, youtube stream or something else.
What video format planned to use? Avi, ogg, mkv, mp4 or something else.
What size of file will be?
What a target browser and OS? Windows and MacOS are very different, IE, Safari, Firefox, Opera, Chrome may cause some additional work?
Do you plan to host site on your own server? Perhaps some specific mods, plugins to be set up.
How would you like to upload video and organize the query?
What video should be played first? Will it be the same each time or will it be chosen randomly?
More complex question: what to do if current played video will be deleted from server?
Of course your task is solve-able, but answer the questions please before.