AVAssetReader, how to use with a stream rather than a file?

AVAssetReader is fantastic, but I can only see how to use it with a local asset, a file, or I guess a composition,

So,

assetReader = try AVAssetReader(asset: self.asset)
...
assetReader.addOutput(readerOutput)

and so on,

Say you have an arriving stream

(perhaps Apple's examples of .M3U8 files,

https://developer.apple.com/streaming/examples/ )

In fact, can AVAssetReader be used for streams? Or only local files?

I just plain cannot find this explained anywhere. (Maybe it's obvious if you're more familiar with it. :/ )

from AVAssetReader, how to use with a stream rather than a file?