A watermark added for audience measurement is most likely to be added by which device?

A watermark for audience measurement is typically embedded at the encoding stage of the broadcast process. This means the correct device responsible for adding such a watermark is indeed associated with the encoding function, which allows for additional data, like watermarks, to be integrated into the media content.

In this context, a NAVE (Networked Audio and Video Encoder) is specifically designed to handle the encoding of video and audio streams and may include functionalities for inserting watermarks. This capability is crucial for audience measurement, as it allows broadcasters to track viewership and analyze data related to how content is consumed.

The other devices mentioned serve different purposes. A decoder is used to convert encoded signals back into a usable format for playback, while a transmitter is responsible for sending out the broadcast signal. Therefore, neither of these is involved in the initial watermark embedding process.