Using mediainfo, how should I calculate video bit rate?

[frobber]

I'm writing some code that needs to parse the output of mediainfo, to get the video bit rate.

I'm asking mediainfo for JSON, and getting over 100 tracks (there seem to be lots of extras on this DVD).

To simplify, I look for the IFO with the longest duration and work from there (assuming that's the "main" title).

The IFO itself has an "OverallBitRate" but the value is very small, e.g. "29". There are several VOBs associated with this IFO, but each one has a slightly different "OverallBitRate", and there are some super-short tracks that have a very different bit rate (e.g., 400 ms duration, with a bit rate that's 1/3 of the other VOBs). Some have a "BitRate" and some have a "BitRate_Maximum", so I'm a little confused by all these different values.

Is there some kind of rule for how this should be calculated ?

TIA !