Google announced advertising changes on Tuesday aimed at strengthening tools for marketers that underscore the Internet behemoth's shift to mobile.

The biggest change that consumers will see will be ads for mobile-app downloads, on Google Search and YouTube. Delivered via the Google display advertising platforms AdWords and AdMob for Search, and TrueView video ads on YouTube, the move indicates that Google is attempting to stem the hemorrhaging from its declining cost-per-click revenue.

In addition to encouraging users to install the promoted app, if the ad network detects that the app already has been installed, the ad will allow the user to open the app from the ad.

Jerry Dischler, Google's vice president of AdWords product management, told an audience of marketers in Half Moon Bay, Calif., that online advertising is no longer device-specific, because consumers use multiple devices simultaneously and seamlessly.

"If there's one thing you take away from my talk today, it's this: It's no longer about devices, it's about connecting people to the content that they care about, whether they're online, on mobile sites, or in apps," he said.

The problem with apps, he said, is that 60 percent are never installed and 80 percent are used only once. Search will suggest keywords to advertisers from Google Play. Apps will be suggested based on related concepts, such as a calorie-counting app suggested to people who have a running app installed. People will also be encouraged to download apps related to videos they're watching. And app "deep linking" will be used, connecting ads directly to content buried within an already-installed app -- an ad for a TV show, for instance, could take you directly to that show on the Hulu Plus app.

The changes, Dischler said, will take "a few months to roll out."

Other changes in Google's tools help marketers manage their ads. Dischler emphasized the helpfulness of Google's new Estimated Total Conversions, which give owners of physical stores a better idea of how digital ads convert to real-world sales. He also spoke of tools like automated bidding and an AdWords "testing lab" for running live tests in already-running advertising campaigns.