as3 video buffer overflow(explosion)

Question

ResolveVideoURL("rtmp://url");


function asyncErrorHandler(event:AsyncErrorEvent):void 
{ 
    trace(event.text); 
} 


function doPlay1() 
{
    //if( vns1 !=null )vns1.close(); vns1 = null ;

    vns1 = new NetStream(vnc1);
    vns1.addEventListener(AsyncErrorEvent.ASYNC_ERROR, asyncErrorHandler); 


    mv1.attachNetStream(vns1);
    //mv1.smoothing = true;
    vns1.bufferTime = 1 ;
    vns1.play(CVL2);

}

function ResolveVideoURL( Url: String  )
{
    var tmpLOC : int = Url.lastIndexOf("/");

    CVL1 = Url.slice( 0 , tmpLOC ); 
    CVL2 = Url.slice( tmpLOC + 1 ); 

    vnc1.connect(CVL1);
}

has anybody ever get video return bufferLength overflow? like below image
it should be very close to 1 , but get a large amount of it
it's encoding use vp6 , 800Kb(flow)
https://i.stack.imgur.com/CO2Ww.png