I have an app in which I use AVAudioEngine for playing files from the local file system by using AVAudioPlayerNodes and AVAudioFiles.
AVAudioEngine
AVAudioPlayerNodes
AVAudioFiles
Apple's documentation doesn't specify if it can work with a mp3 hosted online but as soon as I try to initialize an AVAudioFile with a mp3 url it crashes instantly with a fatal exception. I think that answers your question.
AVAudioFile