Is AVAudioPCMFormatFloat32 required for playing a buffer with AVAudioEngine / AVAudioPlayerNode

I have a PCM audio buffer (AVAudioPCMFormatInt16). When I try to play it using AVPlayerNode / AVAudioEngine an exception is thrown:

"[[busArray objectAtIndexedSubscript:(NSUInteger)element] setFormat:format error:&nsErr]: returned false, error Error Domain=NSOSStatusErrorDomain Code=-10868

(related thread https://forums.developer.apple.com/forums/thread/700497?answerId=780530022#780530022)

If I convert the buffer to AVAudioPCMFormatFloat32 playback works.

My questions are:

1. Does AVAudioEngine / AVPlayerNode require AVAudioPCMBuffer to be in the Float32 format? Is there a way I can configure it to accept another format instead for my application?
2. If 1 is YES is this documented anywhere?
3. If 1 is YES is this required format subject to change at any point?

Thanks!

I was looking to watch the "AVAudioEngine in Practice" session video from WWDC 2014 but I can't find it anywhere (https://forums.developer.apple.com/forums/thread/747008).