Media chiefs will need all of their persuasive powers to win over the Wall Street jury eager for clarity on this key question during the Q4 earnings season that unofficially kicks off this Thursday, when Viacom reports. Many investors are becoming fed up after seeing industrywide TV ad sales continue to fall — an estimated 1.4% in Q4 vs the period last year — while live viewing declined by about 15 minutes.

“The media companies have fostered a storyline of advertisers delaying spending,” Bernstein Research’s Todd Juenger says. “We bought into that storyline throughout the first half of 2014. However, after many quarters have passed, we don’t believe it is valid to continue calling it a ‘delay.’ At some point it has to be a ‘decline.'” He demonstrated his conviction last week by decreasing his earnings estimates for AMC Networks, CBS, Disney, Discovery, Scripps Networks, Time Warner, and Viacom.

Others also are urging clients to lower their expectations, and not just because of ad sales concerns. They see new and growing competition from online services — including Dish Network’s $20 a month Sling TV, which will begin to sign up customers tomorrow. Programming costs also continue to rise as companies produce more original shows, and buy sports rights.

  • Wells Fargo Securities’ Marci Ryvicker just reduced her earnings forecasts for CBS, Fox, Time Warner and Viacom.
  • Yesterday BMO Capital Markets’ Dan Salmon reduced his stock price targets for CBS and Viacom, although he raised for Disney.
  • MoffettNathanson Research’s Michael Nathanson recently cut earnings estimates for Fox and Discovery, while also raising Disney.
  • And last week Morgan Stanley’s Benjamin Swinburne cut price targets for CBS, Fox, Time Warner, Discovery, Viacom, and Scripps Networks.

Nathanson observes that the last quarter of 2014 was the third in a row in which prime time broadcast and cable ratings fell for the target 18-to-49-year-old audience (including viewers who tune in up to three days after a show airs).  What’s more, the 7% drop was “just about the worst decline we have seen,” he says. Nielsen deserves part of the blame, for example for not capturing viewing on mobile devices. Still, “it is not clear that these trends will be reversed over the next could of quarters until the ‘easy compares’ start in mid-2015.”

Investors appear to be listening. The Dow Jones U.S. Media Index is down about 3% since the beginning of 2015, while the benchmark Standard & Poors’ 500 has been virtually flat.