i solved my problem.
before i was adding metadata to my recorded video in "NetStream.Publish.Start" handler like so:
case "NetStream.Publish.Start":
var metaData:Object = new Object();
metaData.title = "test";
metaData.width = cameraWidth;
metaData.height = cameraHeight;
liveStream.send("@setDataFrame" , "onMetaData", metaData);
break;
And changed "NetStream.Record.Start" instead "NetStream.Publish.Start". Now it works fine for me.
I think if you want to playback any recorded stream, when your live stream triggers "Netstream.Record.Start", it is avaible to adding metadata.