Beware, YouTube TV subscribers: For many popular shows you record on your DVR, you’re going to be forced to watch the commercials.

YouTube TV launched in select markets last week at $35 a month, touting more than 50 live channels and an eye-catching “unlimited” digital video recorder stored in the cloud.

But there’s a catch, thanks to the tangle of contracts YouTube has with major media companies like Walt Disney Co., 21st Century Fox and Comcast Corp. ’s NBCUniversal.

Let’s say a subscriber decides to record ABC’s “Blackish” episode in hopes of being able to catch up on it in a few days, skipping over the ads while they watch.

Within 24 hours, though, YouTube likely will have the on-demand version of that show available, since many TV networks offer cable providers at least the last five episodes for catch up on demand. In on-demand versions of shows, TV networks typically disable fast-forwarding over ads to make sure they get credit from marketers who pay for the commercials.

If YouTube TV does have the on-demand version of Wednesday night’s “Blackish” available, then it won’t let its subscribers watch a recorded version that allows for ad-skipping. Instead, viewers will be forced to watch the on-demand episode and all of the ads, even though consumers thought they saved the show on their DVR.

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A YouTube spokeswoman confirmed the arrangement and said it is “tied to deals” with TV programmers. Of course, if the on-demand version doesn’t exist, the YouTube TV subscriber will be able to watch a recorded version and skip ads.

It’s an unusual compromise with TV networks that marks a departure from how traditional cable operators like Comcast operate. Most cable operators tend to offer both the option to watch your recorded show, thereby allowing ad-skipping, or the on-demand version.

Some TV executives said that YouTube’s arrangement is new, and that even Dish Network Corp. ’s Sling TV streaming competitor won’t have that stipulation as it rolls out its cloud DVR service.

Part of what led to the unusual concession on YouTube’s part is that TV networks have been wary of doing deals with the Alphabet Inc. -owned entity, one person familiar with the matter said. YouTube has long had a contentious history with TV networks, many of whom think it hasn’t done enough to battle pirated content appearing on its platform.

Some TV executives indicated that this DVR arrangement is something they’ll push for in future deals with new streaming services offering a package of channels. While it isn’t possible to put the DVR genie back in the bottle for traditional cable customers, TV networks are hopeful they can train viewers to expect ads at least in on-demand, current-season shows they stream.

Write to Shalini Ramachandran at shalini.ramachandran@wsj.com