The NetStream method of playing FLV files was only supported in Flash Player 6 when using Flash Communication Server (now Flash Media Server). So you're client is either going to need to be prepared for long download since you would need to import the full video into the SWF to play it ( importing the video into the SWF will not allow progressive download, it would need to fully donwload before the video would play...), allow the user's to be prompted to upgrade their Flash Player, pony up the $4k or so to install and set up Flash Media Server, or find an online provider that offers FMS.
Of those options, I would think the prompt to upgrade would be the best.
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