Flash movies in inactive browser tabs pause or don't execute in real time

Question

I'm noticing some unexpected behavior. Some time in the last few months, a change in either Firefox, the Flash player, or both, has made it so that Flash movies that are in inactive browser tabs no longer execute in real time. They appear to still execute, but only in bursts, and not in a predictable way. This is a problem because I develop a Flash-based (Actionscript 2.0, Flash CS3) multiplayer game that maintains a network connection and allows players to chat, etc.

Many of our players complain about Firefox crashing while playing the game. I have noticed it too, not too frequently, but it crashes several times a week. (Firefox crashes, I do not get a message from Flash player that indicates an infinite loop or problem in my code) My theory is that this new behavior is causing crashes when there is a lot of activity in my game, leading to lots of unhandled network traffic for my game getting buffered before Firefox/Flash will give it a chance to execute. Maybe this leads to a buffer overflow or missing packets, and as a result, something crashes. At times I will switch back to the tab that is running my game and discover a display bug, which looks as though Flash has simply failed to execute something that it was supposed to. I would assume this new behavior is on purpose, for example to prevent all the Flash-based advertisements in inactive tabs from executing and therefore killing performance.

In a quick test on Chrome (5.0.342.9 beta), this "pausing" of Flash seems to be there as well, but somehow it seems much less of a problem. My users have only complained about Firefox crashing, not other browsers.

My machine:

• Windows 7 x64
• Firefox 3.6.3
• Flash Player 10.1.50.426
• My game: triplejack.com

Any ideas? Ideally I'd like to disable this behavior for my Flash game so it can execute in real time even when in an inactive tab. Thanks for any help!

Answer 1

The Flash Player 10.1 beta 3 made flash movies do less processing when on a hidden tab.

From Tinic Uro's article about the changes:

SWF is Invisible:

• SWF frame rate is clocked down to 2 frames/sec. No rendering occurs unless the SWF becomes visible again.
• timers (AS2 Interval and AS3 Timers) are clocked down to 2 a second.
• local connections are clocked down to 2 a second.
• video is decoded (not rendered or displayed) using idle CPU time only.
• For backwards compatibility reasons we override the 2 frames/sec frame rate to 8 frames/sec when audio is playing.