# Identifying content in an MP4 source
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The content in an MP4 source always consists of one video track, one or more audio tracks, and optional captions. 

Obtain identifying information from the content provider.


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|  Asset  |  Details  | Information to obtain | 
| --- | --- | --- | 
| Video | You don't need identifying information. MediaLive always extracts the single video asset. | None | 
| Audio | The source might include multiple audio tracks, typically, one for each language.  | Obtain the track numbers or three-character language codes of the languages that you want. | 
| Captions | EmbeddedThe captions might be embedded in the video track or might be embedded in an ancillary track. | Obtain the languages in the channel numbers. For example, "channel 1 is French".  |