With about half as many high-definition channels as satellite TV leaders DirecTV and Dish Network, cable providers Cox Communications and Charter Communications are still maintaining their subscription base and sales largely by boosting the number of HD subscribers.

Cox and Charter, the No. 3 and No. 4 U.S. cable TV services behind Comcast and Time Warner Cable, both said this week that they increased video services revenue at least partially by having more high-definition subscribers.

In addition to the satellite companies, the cable companies’ apparent resilience comes amid more competition from fiber-optic television services. Verizon’s FiOS subscriber base surpassed 1 million this year; AT&T’s U-verse is expected to do the same later this year. Like Comcast and Time Warner Cable, Cox and Charter have bandwidth restrictions that don’t affect satellite and fiber-optic operators, keeping their HD channel inventory to between 40 and 50.

Charter increased first-quarter revenue 10% to $1.56 billion as digital video and advanced services such as high-definition programming helped boost video sales. The company also maintained its subscriber base of 5.6 million from a year ago. Like Comcast and Time Warner Cable, Charter showed its biggest gains in high-speed Internet and telephone services, but still had a 2.4% rise in video sales.

“Customers with HD and DVR service increased 50% year-over-year,” Charter CEO Neil Smit said on a conference call this week.

Closely held Cox, with 6.2 million subscribers, said this week its HD subscriber base also grew by more than 50% from a year earlier. The company said it will launch new services from Lifetime Networks, including Lifetime Television HD, Lifetime Movie Network HD, Lifetime on Demand and Lifetime Movie Network on Demand.

Cox will begin rolling out Lifetime HD to subscribers in June.