Thanks a lot!

Hmm.. I think it's quite essential, all DSLR and most compacts have direct access to exposure correction by dedicated buttons, even my old SE k770 phone had mapped it directly to hardware keys. It's extremely useful in back light conditions when you have the sun in front of you, and fast access is critical here (Nokia got this unbelievably wrong with their Symbian touch phones..). Maybe a simpler method than using the volumme keys would be putting two shortcuts on the keyboard (+0.5/-0.5ev), and an indicator on the display if it's != 0?
I've played a bit around with it, and so far I have found two ways to accomplish this:

1)
to stop tracker and to start it again. It's what tracker-cfg uses to restart tracker, but does not empty the database. Seems to work reliable & should be safe. Disadvantage: After restarting, tracker-indexer is active for quite some time (several minutes), eating away some 2% of cpu time on my system. That's a bit strange, as it should not rebuild the database.

2)
to stop/continue the trackerd task. Seems to work well when trackerd is the only tracker task active, in my test it was inactive while filming and immediately started to index after unsuspending it with the CONT signal. When it's already indexing stuff things get more complicated, as other task like tracker-indexer, tracker-extract, gst-video-thumbnailerd appear. So
seems work (just gives an error when a task is not found, but suspends/unsuspends the other tasks, alternatively one could use the output of tracker-processes), but I am not sure if this does not have any unwanted side effects (data corruption etc). Maybe there´s someone more knowledgeable about this here?

Greets
Christian