Is there any way to understand who or at least why a downvote was awarded?
No, not unless the person left a comment - which need not mean that that's the person who cast a downvote.
Answer #1:
Check the compete discussion on this answer: No sound in Flash videosNo sound in Flash videos
This will definitely solve it
This should be a comment, not an answer.
Answer #2:
OP says
I can't really use GUI
.. and yet your answer tells a GUI tool
This is just not acceptable!
No, Voting is anonymous and you should be ready accept any vote - up or down.
If this feature is not yet into use I would like to suggest it!