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Please take a screenshot for the issue and post here.
Please click "restore previous purchases" before you save videos to iTunes.
Don't buy again,just click “Restore precious purchases”
It's a bug, please post your email address here, I will send you a test version to recover the videos.
Visit http://get.udid.io/ on your iPhone, follow the instruction to send your UDID to my email zhustar@gmail.com
When I received your UDID, I will build a test version and send it to you, you want to install it to figure out the issue.
Is there any message when you save videos to iTunes?
I doubt you haven't unlocked the feature, try extract audio from any downloaded video, if it can't be done, it means feature isn't unlocked. You have to restore previous purchases with the account that purchased the item before
An email sent, please check out your email inbox.
Hi Timmer,

I need more details, would you like to help to figure out the problem? It will need you to install a test version to debug.
Yes, is "adonisshera@yahoo.com" your email address? I will send an email to you
The issue can be fixed before the next version but would you like to install a test version manually ?