It’s approximately 1.2MB for 10,000 viewers.

No image or video is ever uploaded.
The uploaded information only includes audience and traffic data, along with some monitoring information (such as the CPU usage, the percentage of light in the scene, etc), which are useful to diagnose potential problems without any image.

For areas with an average traffic of 1000 persons per day, the upload size is thus about 4 MB per month.

Note:
When using the audience per content API, the volume may increase drastically, depending on the clip duration, ID, etc.