trak box ——This is a container box for a single track of a presentation. A presentation consists of one or more tracks. Each track is independent of the other tracks in the presentation and carries its own temporal and spatial information. Each track will contain its associated Media Box.
Track_enabled: Indicates that the track is enabled. 若此位为0，则该track内容无需播放（好比咱们用一些非线编软件<如Sony Vegas>作视频剪辑时，有些Track仅为咱们参考与模仿用，在输出时将该Track关掉）。 Track_in_movie: Indicates that the track is used in the presentation. Track_in_preview: Indicates that the track is used when previewing the presentation.
Track_in_poster: Indicates that the track is used in movie's poster.