How can I use BitmapData.draw with NetStream.appen

Question

I am using NetStream.appendBytes() to play a local video (no server involved) in Adobe AIR. I would like to use BitmapData.draw() to take a picture of the video output, but I am getting this error:

Error #2123: Security sandbox violation: BitmapData.draw: cannot access null. No policy files granted access.

Here is some sample code:

package
{
    import flash.display.Sprite;
    import flash.filesystem.File;
    import flash.filesystem.FileMode;
    import flash.filesystem.FileStream;
    import flash.media.Video;
    import flash.net.NetConnection;
    import flash.net.NetStream;
    import flash.net.NetStreamAppendBytesAction;
    import flash.utils.ByteArray;
    import flash.display.BitmapData;

    class ByteArrayPlayer extends Sprite
    {
        private var _ns:NetStream;
        private var _nc:NetConnection;
        private var _video:Video;

        public function playVideo(path:String):void
        {
            _nc = new NetConnection();
            _nc.connect(null);
            _ns = new NetStream(_nc);

            _video = new Video();
            addChild(_video);
            _video.attachNetStream(_ns);

            _ns.play(null);
            _ns.appendBytesAction(NetStreamAppendBytesAction.RESET_BEGIN);

            var file:File = new File(path);
            var fileStream:FileStream = new FileStream();
            fileStream.open(file, FileMode.READ);

            var bytes:ByteArray = new ByteArray();

            fileStream.readBytes(bytes);

            _ns.appendBytes(bytes);
        }


        public function getImage(video:Video):BitmapData
        {
            var bit:BitmapData = new BitmapData(_video.width, _video.height);
            bit.draw(_video);            //This will cause the error
            return bit;
        }
    }
}

This is only sample code use for an explanation. The error would happen when calling the getImage method while the video is playing. The error mentions a policy file not found. Since the file is loaded locally there isn't really a place to put a policy file. Is there a policy setting somewhere that needs to be set or is the BitmapData.draw feature just not available when using appendBytes?

Answer 1

Try set NetStream.checkPolicyFile = true before you call the play() function.

Like this:

_ns.checkPolicyFile = true;
_ns.play(null);

What the checkPolicyFile flag does is that it tells the host swf to load a policy file from the loaded swf's server. If you haven't specified that flag at loading time you will recieve a SecurityError when you try to get pixel data from the loaded stream through BitmapData.draw().

Link to Adobe resource: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/net/NetStream.html#checkPolicyFile