Hey Will, we did some testing with Exacq and Hikvision as two examples.
Export size is approximately equal the the stream size for a the given time. Video only exports (.mp4, .avi, etc.) didn't add significant file size overhead, and both Hikvision and Exacq .mp4 exports were approximately the same size. Exacq's standalone player is about 13MB in addition to the clip video itself. Hikvision doesn't offer a standalone export player.
That being said, determining an "average" depends on so many factors that it is almost useless as an actual metric, as it depends on scene activity, codec used, smart codecs, sharpness, WDR performance, digital noise reduction, and any number of other issues which vary widely from model to model and scene to scene. For example, a 1080p10 camera might use as little as 12 Kb/s in a still scene, using H.265, dynamic I-frames, dynamic compression. etc. While another current generation, high end model uses over 1 Mb/s, 2 Mb/s or possibly more.
Because of this, we can give guidelines, but hard and fast averages would be misleading. Our reports Calculating Video Surveillance Storage / Bandwidth and Video Surveillance Bandwidth Guide give recommendations for how to best estimate for your camera(s) and scene(s).
We hope to do some more standardized bandwidth testing in various scenes in the coming months, so we can provide more guidelines, also.