When a audio file is downloaded in a remote playback situation and we receive no ContentType header, we derive the content type from the extension of the filename. But some servers send application/octet-stream as ContentType, which is currently rejected and leads to a playback error. Therefore I think - even though browsers do not play back application/octet-stream audio file types - we could support playing back them by treating the application/octet-stream exactly like in a situation no ContentType header is received.