Dolby Audio Processing is supported only by nPlayer Plus version that uses an officially certified Dolby audio. When playing Dolby Digital(AC3) audio codec file in nPlayer, you can use DTS Headphone:X for sound effect. Please refer to this link for the details about the nPlayer product specifications.
Dolby Audio Processing
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Play a Dolby Digital(AC3) audio codec file.

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Touch DOLBY AUDIO mark on the bottom right of the playback screen.

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Activate Dolby Audio Processing, enjoy your video with Dolby sound effect.

DTS Headphone:X
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Play a DTS or any kind of audio codec file.

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Touch DTS Headphone:X mark on the bottom right of the playback screen.

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Activate DTS Headphone:X, and set up the Stereo Preference, Accessory and Equalizer.

* Video files in Album or iTunes folder of Local tab can only be played via QuickTime and cannot be transmitted to Smart TV or Chromecast. And the sound effects functions such as DTS Headphone:X, Dolby audio processing is not applied. However, if you copy video files to Document and play, you can use them.