The Chromecast's playing principle is, if nPlayer sends a file to the Chromecast, playback is done by the Chromecast. Chapters are not activated because Chromecast do not support it. Please take considertation into this.
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Not all videos and audios available on nPlayer can be played on Chromecast but only those that meet the standard of Chromecast can be. Please refer to the below link for the details.