[fljot]

// retrieve the FLV stream
var bytes:ByteArray = event.currentTarget.data;
// put the NetStream class into Data Generation mode
netstream.play(null);
// before appending new bytes, reset the position to the beginning
netstream.appendBytesAction(NetStreamAppendBytesAction.RESET_BEGIN);
// append the FLV video bytes
netstream.appendBytes(bytes);

from http://www.bytearray.org/?p=1689

where

var bytes:ByteArray = screenCapture.data;

in your case. Give a try.