NYTs' Brian Stelter writes about the huge, multi-million visitor discrepancy regarding Hulu.

While Nielsen reported 8.9 million visitors to Hulu in March, another measurement firm, comScore, counted 42 million. Exacerbating the confusion, Nielsen's numbers for April show Hulu losing audience while still managing to add video views, also known as streams.

The wildly divergent numbers demonstrate the nascency of the market for online video measurement. It's "still the wild wild West," said Rob Davis, a leader of the interactive video practice at OgilvyInteractive.

Stelter obtained an e-mail exchange between Nielsen and Hulu staffers, which spells out Hulu's frustration with Nielsen's "extrapolation of the unique visitor number."

The staff members complained that reporters and media buyers frequently used the Nielsen data to describe the audience for Hulu, sometimes in negative ways.

Hulu declined to comment on the e-mail messages. But in a statement, Jean-Paul Colaco, the senior vice president for advertising at Hulu, said "there is more work that can be done with all of our research providers to ensure that online video metrics are accurately represented to users and clients."

Stay tuned.