Comcast's Xfinity Mobile service is imposing new speed limits on video watching and personal hotspot usage, and the company will start charging extra for high-definition video over the cellular network.

The short version is that videos will be throttled to 480p (DVD quality) on all Comcast mobile plans unless you pay extra, while Comcast's "unlimited" plan will limit mobile hotspot speeds to 600kbps. Only customers who pay by the gigabyte will get full-speed tethering, but the cost would add up quickly as Comcast charges $12 for each gigabyte.

Comcast last year began selling mobile plans with data, voice, and texting. Comcast doesn't operate its own cellular network, so it resells Verizon Wireless service.

The new speed limits could help Comcast save money on the reselling fees it pays Verizon. In a statement to Ars, Comcast said it's making the changes "to help us maintain the low price point of Xfinity Mobile." While Comcast doesn't control the Verizon network and thus can't impose speed limits directly, Comcast told Ars that Verizon offers resellers an option to limit video resolution.

Comcast said that 480p "is consistent with standard unlimited plans across carriers," and that it's making the changes to bring Comcast's offerings in line with the rest of the industry. Verizon began throttling mobile video to 480p or 720p on smartphones last year; the system limits the amount of bandwidth available to anything identified as a video. Carriers argue that many consumers can't tell the difference between 480p and higher quality on smartphone screens.

Customers get bad news in email

Comcast has been telling Xfinity Mobile customers about the changes in an email titled, "Update on cellular video resolution and personal hotspots." One Comcast customer forwarded the email to Ars, and there's also a Reddit thread discussing the email. All Xfinity Mobile customers are receiving this email, Comcast confirmed to Ars.

"To help you conserve data, we've established 480p as the standard resolution for streaming video through cellular data," Comcast told customers. For now, customers can contact Comcast for an "upgrade" to 720p video "on an interim basis at no charge."

But after the interim period is over, getting HD-quality video will cost extra. "Later this year, 720p video over cellular data will be available as a fee-based option with your service," Comcast told customers. Comcast hasn't mentioned any plans to make 1080p or any resolution higher than 720p available over cellular, and there's no word from Comcast yet on what enabling 720p video will cost. Comcast previously imposed no speed limits on video streaming on the Xfinity Mobile service.

"It's important to note that this change won't impact video resolution when using Wi-Fi, where customers will continue to be able to stream in HD," Comcast told Ars. Over Wi-Fi networks, including Comcast's public hotspots, video will play at whatever resolution is streamed by the video provider, a Comcast spokesperson told Ars. Nearly half of videos that stream on Comcast's mobile service play at 480p today, according to the company.

The Comcast email also directs customers to an FAQ describing the video changes.

Unlimited plan’s tethering limit

While the video throttling applies both to Comcast's limited and unlimited service plans, the new tethering speed limit only applies to the unlimited plan.

"If you have the Unlimited data option, your speeds on any device connected to a personal hotspot will not exceed 600kbps," Comcast told customers. Xfinity Mobile users can get 4G hotspot speeds by switching to Comcast's "By the Gig" pricing.

By the Gig customers pay $12 for each gigabyte of usage. The unlimited plan costs $45 a line each month, and it's unlimited in the sense that there are no overage fees for using too much data. But the unlimited plan only provides 20GB of full-speed data each month—after 20GB, the plan is limited to 1.5Mbps downstream and 750kbps upstream at all times. This limitation was already in place when Comcast started offering mobile service last year.

Comcast only sells mobile service to customers who subscribe to Comcast home Internet.

Comcast: Speed limits are good for you!

While Comcast is imposing the video and hotspot changes shortly after the repeal of net neutrality rules, the rules may not have stopped this form of throttling. The rules banned throttling, but they had an exception for "reasonable network management." The major wireless carriers have imposed various video and hotspot limits on their mobile networks without being punished by the Federal Communications Commission.

Comcast is trying to convince customers that the new speed limits will be good for them. The 480p video limit "can help you save money if you pay By the Gig," and it could help unlimited data customers stay under the 20GB throttling threshold, Comcast told customers in the email.

On the 600kbps tethering limit, Comcast told customers, "At this speed, you'll conserve data so that it takes longer to reach the 20GB threshold, but you'll still be able to do many of the online activities you enjoy."