Video Volume very low after 7.1 on Iphone 4

After Upgrading my IPHONE 4 to ios 7.1, all Videos recorded have a very low volume.

Microphone works very well, infact all other audio-recording applications (internal and external from ios) are ok both in recording and reproducing.

The problem, so, is the software.

I've tryed an hard reset and I have checked all volume levels.

I've tested this problem on two different Iphone 4 and they have the same bug.

Anyone else?