We are a couple of software developers and were planning on making some commercial extension or some website through which users, with slow internet connections or limited data could play almost any video through YouTube's API. Although, while going through the API docs, we came through the following section,
Your API Client will not, and You will not encourage or create functionality for Your users or other third parties to:
"separate, isolate, or modify the audio or video components of any YouTube audiovisual content made available through the YouTube API"
-Kuan Yong, YouTube API Team
Is there no such legal way through which we can disable just the video and stream audio, not even with the commercial API?
Hoping for a positive reply.
Playing just audio means isolating audio, which is a clear violation of the terms and conditions of the YouTube API. However, as far as I know, there is no such restriction when not using the YouTube API. For example, youtube-dl, which is a video downloader for YouTube and hundreds of other websites, has the functionality to download just audio.
In fact, in YouTube's format, audio and video are actually stored in separate files on the server. This means you can actually acquire the path to the audio file and stream it to you users. Check out the open-source youtube-dl, specifically the youtube module, for more details.
Edit
The reason I am merely linking to a library is that YouTube continually changes the way they format, store, and stream video. This means that retrieving the direct link to a video's audio component is a task subject to frequent change. If you can link against youtube-dl's python module, you can make use of their updates whenever such changes occur.
Disclaimer
I am not fully sure if this is all legal and whatnot. Hence, I take no responsibility for your decision on what to do, nor do I condone this kind of behavior.