public function testVideos()
 {
     $audio = $this->getStreamMock();
     $audio->expects($this->once())->method('isVideo')->will($this->returnValue(false));
     $video = $this->getStreamMock();
     $video->expects($this->once())->method('isVideo')->will($this->returnValue(true));
     $collection = new StreamCollection(array($audio, $video));
     $videos = $collection->videos();
     $this->assertInstanceOf('FFMpeg\\FFProbe\\DataMapping\\StreamCollection', $videos);
     $this->assertCount(1, $videos);
     $this->assertEquals(array($video), $videos->all());
 }