The United States lags behind dozens of other countries when it comes to the quality of streaming video available to mobile users. And according to a new report from mobile network testing company OpenSignal, that’s in part because most U.S. carriers throttle the quality of the video streaming over their networks.

“Video experience can also be heavily impacted by operator policy. Many operators globally use video optimization technologies to restrict the level of video resolution their customers can access on their phones. As our tests sample video at different resolutions, any downgrading of video quality—say from HD to SD—would have an impact on our scores,” OpenSignal wrote in its new report. “The U.S. is a prime example of such policies at work.”

OpenSignal historically has measured the upload, download and latency speeds provided by mobile networks around the world, mainly via apps installed on users’ phones. But in its latest report the firm expanded into the video streaming realm by looking at three main video criteria: the load time before the video begins playing, the stops and stutters in the video playback, and the level of picture resolution. The firm recorded almost 90 billion measurements across 8 million phones globally from May to August in its latest report, and combined all those data points to calculate a mobile video streaming quality rating it applied to the services in 69 different countries.

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The company found that the United States came in near the bottom of the rankings with an overall score of around 47. (75-100 is Excellent, 65-75 is Very Good, 55-65 is Good, 40-55 is Fair and 0-40 is poor.) Topping the rankings was the Czech Republic with a score of around 68. The United Kingdom scored at 60 and Kazakhstan scored at around 48.

OpenSignal did not break its results out by wireless operator.

Importantly, OpenSignal noted that the overall speed provided by mobile network operators in the countries it surveyed didn’t necessarily lead to good mobile video streaming scores. The firm said that after around 20 Mbps, video quality did not improve with faster speeds—for example, South Korea’s operators provided the fastest overall recorded speeds at around 45 Mbps but the country’s video score came in at around 63, outside of the top 10.

OpenSignal said more important factors for video streaming quality were latency, consistency and network reliability.

As for the United States, OpenSignal said the country “lands in the middle of the Fair range of video experience with a score of 46.8, but its average overall download speed of 16.5 Mbps suggests it should have scored much higher in video experience.”

The firm continued: “To prevent their networks from becoming overloaded with video traffic, [U.S.] operators have put streaming restrictions on their different tiers of unlimited plans. For many users on unlimited plans in the U.S., the highest resolution video they can stream over a mobile connection is 480p.”

But the firm said that the country’s score might not improve if operators stopped throttling video quality.

“Depending on the type of video, a 720p stream can consume twice as much or more data than a 480p stream,” OpenSignal wrote. “And as video now accounts for the majority of all mobile internet traffic, a doubling of the gross tonnage of video consumption would have a major impact on any operator's network. More traffic leads to congestion, and congestion not only impacts overall speeds available to consumers but can also lead to inconsistent connections and poorer latencies—all of which have a bearing on video experience. Ironically, if U.S. operators were to lift video restrictions on their unlimited plans, it’s possible that the typical video experience in the U.S. might suffer more.”

Indeed, OpenSignal CEO Brendan Gill told MWL that more operators across the world will likely embrace such throttling techniques as video streaming becomes more popular in other countries.

OpenSignal isn’t the only mobile test company to look at streaming video. For example, AT&T provided the most reliable streaming video service in Global Wireless Solutions’ recent nationwide drive tests of top carriers’ mobile networks. The testing company said that 98% of videos streamed over AT&T’s network were successfully completed, and that videos tested on AT&T only froze 0.82% of the time.