T-Mobile USA's controversial "Binge On" program is throttling all HTML5 video streams and direct video downloads to about 1.5Mbps, according to tests run by the Electronic Frontier Foundation (EFF).

Binge On, unveiled in November, is enabled by default for all T-Mobile customers and downgrades video resolution to 480p in order to reduce data usage. Companies that cooperate with T-Mobile can stream video without counting against customers' high-speed data limits. That means you can watch Netflix, HBO, Hulu, and about another 20 services without using up your data.

But all video is downgraded, regardless of whether it gets a data cap exemption, which has led to a rift between T-Mobile and Google's YouTube.

There's no net neutrality rule that explicitly bans exempting certain types of content from data caps, but there is a rule against throttling. The Federal Communications Commission has asked T-Mobile to meet with commission officials this month to discuss whether Binge On conflicts with "the Commission's goal of maintaining a free and open Internet."

T-Mobile never denied that it was downgrading all video and points out that customers have the option of disabling Binge On. But T-Mobile didn't provide many details of how it's throttling video, which led the EFF to perform some tests. The EFF said it posted a video on one of its own servers and tried accessing it from a T-Mobile device.

While video streaming and video downloads were limited to about 1.5Mbps with Binge On enabled, streaming without Binge On was measured at nearly 5Mbps.

"Each test was done over an HTTP connection, which allowed T-Mobile’s network to observe the content of the connection and perform 'optimization' (labeled 'Binge On' in the graph below), and over an HTTPS connection, which prevented T-Mobile’s network from observing the content of the connection, thus representing behavior without any sort of Binge-On-related optimization ('Normal')," EFF Staff Technologist Jeremy Gillula wrote today.

"The first result of our test confirms that when Binge On is enabled, T-Mobile throttles all HTML5 video streams to around 1.5Mps, even when the phone is capable of downloading at higher speeds, and regardless of whether or not the video provider enrolled in Binge On," EFF wrote. "This is the case whether the video is being streamed or being downloaded—which means that T-Mobile is artificially reducing the download speeds of customers with Binge On enabled, even if they’re downloading the video to watch later. It also means that videos are being throttled even if they’re being watched or downloaded to another device via a tethered connection."

T-Mobile is also throttling video downloads when the filename and HTTP Content-Type header indicate that the file isn't a video, EFF said.

"We asked T-Mobile if this means they are looking deeper than TCP and HTTP headers, and identifying video streams by inspecting the content of their customers’ communications, and they told us that they have solutions to detect video-specific protocols/patterns that do not involve the examination of actual content," Gillula wrote.

Throttling semantics

T-Mobile says that video providers must meet the carrier's "technical criteria" to qualify for streaming that's exempt from data caps. T-Mobile has also claimed that it isn't doing any "throttling," that it's actually just "optimizing" video.

However, the EFF said its tests showed that this is nothing but throttling and that the throttling of video occurs even when the T-Mobile network doesn't appear to be congested.

"T-Mobile’s 'optimization' consists entirely of throttling the video stream’s throughput down to 1.5Mbps," the EFF wrote. "If the video is more than 480p and the server sending the video doesn’t have a way to reduce or adapt the bitrate of the video as it’s being streamed, the result is stuttering and uneven streaming—exactly the opposite of the experience T-Mobile claims their 'optimization' will have."

T-Mobile confirmed to the EFF that it isn't doing any optimization of video streams other than reducing their bandwidth, the EFF wrote.

We contacted T-Mobile about the EFF's findings today but haven't heard back yet.

Though Binge On is enabled by default, customers can shut it off in their account settings. The EFF argues that Binge On should be opt-in instead of opt-out, "with clear disclosure that opting in will throttle all video traffic." T-Mobile could also address complaints from video providers by only throttling the video of providers who signed up for Binge On, the group said.