Words matter. YouTube says T-Mobile US is throttling its video. T-Mobile US has not directly responded, but T-Mobile US does process video, as part of its Binge On program, for bandwidth efficiency, in ways that can reduce image quality. The trade-off is that viewing Binge On video does not count against mobile data usage.
YouTube is not part of Binge On, so some think the issue is that T-Mobile US has not yet figured out a way to identify YouTube video content, one way or the other.
So is video encoding, for better bandwidth efficiency, at the risk of lower image quality, throttling or only processing?
Some might argue, oh by the way, that processing media types for better performance (lossless) is a good thing. Image degradation that is not asked for, or wanted, is not a good thing. But Binge On partners have agreed to have their video processed as part of the program.
Nor, some would argue, should content providers be prohibited from coding that actually boosts image quality or loading times. That is, after all, what they pay Akamai and others to provide.