NEW YORK: Some major advertisers are reported to have reduced the total dollars they have committed to the 2015 upfront ad-selling season, as one newspaper cited "tectonic shifts in the very nature of ad-buying".

"I think that the overall ad volume will come in modestly worse than expected," John Janedis, an analyst at Jefferies & Co, told the Wall Street Journal.

"Marketers are holding back more dollars than we expected."

Among those marketers, according to the WSJ, are Verizon Wireless, McDonald's and State Farm, although none were prepared to comment.

Janedis had predicted spending declines similar to 2014, when there was a 6% drop in cable ad commitments and a 5% drop in broadcast commitments.

Previously, Vijay Jayant of Evercore ISI estimated that broadcast networks would complete the upfronts having sold 69% of their inventory, compared to 73% last year.

The comparable figures for cable networks showed a slower decline, from 51% to 49%, MediaPost reported.

The WSJ also noted that TV networks have been redefining what counts as upfront spending in an attempt to boost their figures. As a result, content creation deals, social media offers and syndication are all being added to the totals, making like-for-like comparisons increasingly difficult.

But it is clear that traditional TV advertising is under ever greater threat from other channels, including ad-free platforms such as Netflix.

The latest Global Marketing Index (GMI) from World Economics revealed that the allocation of marketing budgets assigned to TV fell for the seventh month in a row in June, with an index value of 46.8, below the 50.0 "no change" level.

TV's declining fortunes were particularly severe in the Americas, with an index value of only 40.1; the last month of TV growth in this region was recorded 12 months ago.

The hope among the networks is that marketers are holding some money back to buy ad time in the "scatter" market nearer to the date of airing.

In the past, such inventory was sold at a higher price, but with this airtime no longer able to command as much of a premium, there is less pressure on advertisers to seek early deals in the upfronts.

Data sourced from Wall Street Journal, MediaPost; additional content by Warc staff