Question

So we have flv file, we play it with mx:vidodisplay for example. how to get on which stream frame we are currently on?

Answer 1

you can check the nearest keyframe to the current time in stream metadata
upd
when creating a stream you need to handle its’ onMetaData call:

private var metaInfo: Object;

private function initStream():void{
     stream = new NetStream(conn);
     stream.bufferTime = 5;            
     stream.addEventListener(NetStatusEvent.NET_STATUS, onStatus);
     stream.client = new Object();
     stream.client.onMetaData = onMetaData;/*this is what you need*/
     video.attachNetStream(stream);
}
private function onMetaData(info:Object):void {
    metaInfo = info;
    var tmpstr:String = '';
    for(var s:String in info){
       var tstr:String = s + ' = ' + info[s] + '\n';
       tmpstr += tstr.indexOf('object') == -1 ? tstr : '';
       for(var a:String in info[s]){
           var ttstr:String = s + ':' + a + ' = ' + info[s][a] + '\n';
           tmpstr += ttstr.indexOf('object') == -1 ? ttstr : '';
            for(var c:String in info[s][a]){
                var tttstr:String = s + ':' + a + ':' + c + ' = ' + info[s][a][c] + '\n';
                tmpstr += tttstr.indexOf('object') == -1 ? tttstr : '';                     
            }
        }
    }
    trace(tmpstr);          
}

in this trace you’ll see if the streams’ metadata has items like:
seekpoints:93:offset = 10342550
seekpoints:93:time = 165.799

or maybe:
keyframes:times = 0,0.48,0.96,1.44,1.92,2.4,2.88,3.36,3.84,4.32,4.8,5.28,5.76,6.24
keyframes:filepositions = 1063,95174,136998,176043,209542,239148,271062,302006,331724,363948,395039,427503,456317,483313

it depends on encoder settings, if your metadata has any object of this kind (metadata['keyframes'], metadata['seekpoints'] etc) you can do the following:

for (var i:int = 0; i < metaInfo['keyframes']['times'].length; i++) {
    if (stream.time < metaInfo['keyframes']['times'][i]) {
        var keyFrameNum: int = (metaInfo['keyframes']['times'][i] - stream.time < stream.time - metaInfo['keyframes']['times'][i - 1]) ? i : i - 1;
    }
}