Viacom and CBS will need to get bigger even if the two do merge in order to better compete with tech giants, said media mogul Shari Redstone, who controls the two big entertainment companies.

While the companies would be stronger together, ultimately they will need additional leverage in an increasingly competitive media landscape with or without a merger. “We would want to look at something after that to ...develop more scale as we move forward,” Ms. Redstone said in a rare interview on stage at The Information’s Women in Tech, Media and Finance conference Tuesday.