Unity – Build – Web Player

0. MAIN TOP MENU> File> Buil Settings> Select Web Player

1. MAIN TOP MENU> File> Buil Settings> ‘Player Settings’> Inspector to setup

2. MAIN TOP MENU> File> Buil Settings> ‘Build’> Scenes in Build> DRAG AND DROP the _Scenes> YourScene

3. 2. MAIN TOP MENU> File> Buil Settings> ‘Build’> Create Folder ‘Builds/space_shooter’> Save

Web Player Streaming

1. MAIN TOP MENU> File> Buil Settings> check ‘Streamed’
2. MAIN TOP MENU> File> Buil Settings>’Player Settings’> Inspector> Other Settings> First Streamed Level

Advantage:

1. If there is a fast download of the first level you will not see the loader progress bar
2. Not annoing download time improves web gaming experience for the end user

This is the best way:

50 KB display the logo and menu (4 seconds)
320 KB let the user play a tiny tutorial level or let him do some fun interaction in the menu (20 seconds)
800 KB let the user play the first small level (50 seconds)
Finish downloading the entire game within 1-5 MB (1-5 minutes)

There is no reason why all music must be available when the game starts. Externalize the music and load it via the WWW class

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Reference:
http://docs.unity3d.com/Documentation/Manual/WebPlayerStreaming.html