VH preview video player - how does it work?

Can someone explain how the preview video player works?

When does the server converts the videos or at what circumstance the player plays it as it is?

Or does the reviewers have the ability or option to convert the video or they can choose not to convert the video?

Whats the optimal video bitrate and size for the player to upload?

I tried to render my preview video at lowest bitrate which is only 4Mbps but with optimal quality, because i thought the player plays it as it is. But after the approval the preview video was converted to lower bitrate then 4Mbps, which results very poor quality.

Is there any documentation or instruction about this topic? I can only find just the few words where it says “create smaller size .flv or .mp4” as we all know.