//選択したフレームのスパンを指定

var newDuration = prompt('set new duration')
var timeline = fl.getDocumentDOM().getTimeline();
var frames  = timeline.getSelectedFrames()


var startFrames = [];
for(var i=0;i<frames.length;i+=3){
	var layer = timeline.layers[frames[i]];
	var startIndex = frames[i+1];
	var endIndex = frames[i+2];
	for(var k=startIndex;k<endIndex;k++){
		var startFrame = layer.frames[layer.frames[k].startFrame];
		if(startFrames.indexOf(startFrame) < 0)startFrames.push(startFrame);
	}
}
for(i=0;i<startFrames.length;i++){
	startFrame = startFrames[i];
	startFrame.setMotionObjectDuration(Number(newDuration),true);
}