Using Amazon S3 to Host Flash Videos... Why does the FlashVar show no file extension?

I'm using FlowPlayer to replace an existing FLV player on my site that plays videos from Amazon E3.

I have many pages and each should show a different video.

For each page, I have a value stored in my CMS that is the "streamName".

The stream name corresponds to a flashvars paramenter in the object/embed tags that show the video player:

&streamName=my-great-video

On my new player, I'm able to get the video using a URL similar to

https://mygreatsite.s3.amazonaws.com/my-great-video.swf?{$authentication_params}

How Does Flash (or Amazon???) know to add in the .swf extension?

There are several video formats used on the site, and the current player wor开发者_StackOverflow中文版ks with them all... But, as I mentioned above, on each page the value store for the video (ex="my-great-video") includes no extension.

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if it's working without supplied extension then a wild guess is: whatever is parsing the querystring has logic to attempt the GET using an assortment of supported extensions [swf, flv, mp3] if one isn't seen?