It seems that you are confusing streaming and downloading media files from the server.
If we talk about live stream:
1) The file extension does not affect the ability of the AVPlayer player (AVPlayer plays audio from this link, for example: http://icecast.omroep.nl/radio1-bb-aac ).
2) However, the file format does matter (for more information check the docs here ):
What are the features of the supported video and audio formats?
Although the protocol specification does not limit video and audio formats, the current Apple implementation supports the following formats:
Video: H.264 3.0 basic level, 3.1 basic level, 3.1 basic level and 4.1 high profile level. Audio: HE-AAC or AAC-LC up to 48 kHz, stereo MP3 audio (MPEG-1 Audio Layer 3) from 8 kHz to 48 kHz, stereo audio AC-3 (for Apple TV in pass-through mode only)
If you have your own server and want to provide the ability to stream audio / video, you need to perform some configuration steps, as described here .
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