Once the problem occurred, it cannot be solved by re-installing Flash player, clearing Safari history, nor clearing Safari Cookie.
I found a temporally solution.
- Change the USER-AGENT of Safari other than [Safair 4.0.5 - Mac] (for example, [Safari 4.0.5 - Windows]) from [Develop] menu
If [Develop] menu item on your Safari, use [Preferences...] => [Advanced]
Other solutions are exists, but I think there are some disadvantages;
- Change the Safari application from 64-bit to 32-bit
Apples decided the default is now 64-bit. If you forget to switch back from 32-bit to 64-bit, performance penalty or missing new features will become the problem.
- Change the YouTube to HTML5 mode
You can change YouTube to HTML5 mode by visiting youtube.com/html5 . If the html5 version of video is provided, the problem will be solved. Some or many videos are Flash (FLV) only.
- Use embed mode of YouTube
If the url is
then, rewrite it as
You can watch the video in Safari windows as full scaled.
I do not know the problem came from the Flash War, I hope Apple or YouTube solves the root cause early.
[2011-02-21 2:50 JST] Added 4th solution.