TV-streaming service Roku Inc. (ROKU) on Thursday forecast second-quarter sales that were above expectations, but warned of a higher bar for growth up ahead and moderating profit in the second half of the year. Roku said it expected second-quarter sales of $935 million, above FactSet estimates for $926 million. But executives said that “Looking ahead, we face difficult year-over-year growth rate comparisons within streaming-service distribution activities. This headwind is due to past price increases and a higher mix shift toward ad-supported offerings.” Roku reported first-quarter sales of $882 million, up 19% year over year, with a net loss per share of 35 cents. Both were better than expected. Shares were up 2.6% after hours.