How to encode TrueHD 7.1 to DD+ 7.1

Hi,

I'm using Adobe Media Encoder CC 2017 v11.0 and able to encode DTS HDMA/TrueHD 5.1 (6 channels) to DD+ 5.1 without any problems.

But unable to encode 7.1 sources. I converted the source to WMV file which sized around 8.7GB but after importing WMV file, it shows only 7 minutes instead of actual length (2+ hours).

Pls advise, thanks!