You can protect your content from clients that aren't running in Flash Player, based on the user agent string received from the connection. The user agent string identifies the platform and Flash Player version, for example:

WIN 8,0,0,0
MAC 9,0,45,0

There are two ways to access these strings:

Virtual keys 

Configure the server to remap the stream based on the Flash Player client. For more information, see Multiple bit rate switching and VirtualKeys.

Client.agent 

Challenge the connection using Server-Side ActionScript:

application.onConnect = function( pClient ) {
    var platform     = pClient.agent.split(" ");
    var versionMajor = platform[1].split(",")[0];
    var versionMinor = platform[1].split(",")[1];
    var versionBuild = platform[1].split(",")[2];
}

// output example
// Client.agent:  WIN 9,0,45,0
// platform[0]:   "WIN"
// versionMajor:  9
// versionMinor:  0
// versionBuild:  45