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# trackID

An integer that identifies the track within the media asset.

```
var trackID: CMPersistentTrackID { get }
```

## Discussion

The track ID uniquely identifes the track within a [`MEFormatReader`](/documentation/MediaExtension/MEFormatReader) object. Track IDs must be unique within a media asset but don’t need to be unique across assets. If a media format doesn’t have a native concept of track IDs, track IDs can start from `1`. However, track ID `0` is a reserved value to indicate an invalid track ID.

---

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