Ok, so, let me provide a little background on the topic, I've built an app that mimics the Youtube app, except upon selecting a video it connects to one of the various youtube to mp3 converter sites, and streams the audio it provides based on the video id.
I must note that the app does use the Youtube API, but only for fetching video/playlist details.
I tried to publish the app on the Google play store, and was rejected with the following reason, which they pulled straight from their TOS:
We have determined that your app enables background playing of YouTube videos, which is a violation of the YouTube API Terms of Service:
"Your API Client will not, and You will not encourage or create functionality for Your users or other third parties to: (8) separate, isolate, or modify the audio or video components of any YouTube audiovisual content made available through the YouTube API".
I tried to explain to them how the app works but they provided generic responses and eventually cut the communication on the subject.
My question is, why was the app illegal? As the site in which the app connects to fetch the audio works without my implementation (it has its own UI), and I have no ownership/control over the site.
It could even theoretically provide random audio files for every video, would that still be count violation of the TOS?
I know that Google has every interest to not allow these kind of apps on their app store, as it hurts Youtube revenue, I just wanted to know if the statement they provided was enough to reject my application.