a problem of requestThumbnailImagesAtTimes

var playview = Ti.UI.createView({
    width:Ti.UI.SIZE,
    height:Ti.UI.SIZE
});
var player = Titanium.Media.createVideoPlayer({
    height: Ti.UI.FILL,
    scalingMode : Titanium.Media.VIDEO_SCALING_ASPECT_FIT,
    width: Ti.UI.FILL,
    url:Ti.Filesystem.tempDirectory+fileName,
    autoplay:false
});
playview.add(player);
player.requestThumbnailImagesAtTimes([0.0],Ti.Media.VIDEO_TIME_OPTION_NEAREST_KEYFRAME,function (e) {
    player.cancelAllThumbnailImageRequests();
    Ti.API.info(e);
    var image = e.image;
    Ti.API.info(e);
    var imageBlob = image;
    Ti.API.info(e);
    var images = [];
    Ti.API.info(e);
    images.push(mediaItem);
});

When I got the video thumbnails using requestThumbnailImagesAtTimes?if add some output in the callback function?every time can obtain the thumbnail?if remove the output?It is not necessarily obtain thumbnails