Display video file from mongodb with grids-stream.js and express.js 4

I begin to use driver of mongodb grid-stream.js with node.js to my DB store. Everything was good except when I try display my video stored in mongodb. It shows as if it were a file download. This is the code that I have:

function SendFile(res,id){

    var readStream=gfs.createReadStream({
        _id:id
    }).on('open',function(){
        console.log("start..");

    }).on('data',function(chunk){

        console.log('loading..');
        //loading...

    }).on("end",function(){

        console.log("ready");
        //loaded :)

    }).on('error', function (err){

        res.send(404);//no found :(
        console.log(err);

    });

    readStream.pipe(res);

};

app.get("/:video",function(req,res){

    SendFile(res,req.params.video); 

});//get file video

//i think the line readStream.pipe(res); is the problem I think that behaves like res.download but a need to behave like:

Video example