【1/19/2017 Update】
The following option has been added to the "Resume（Continue）" feature offered on the HTML 5 video watch page (β) (released Thursday 12/8/2016).
Turn "Resume" feature On or Off from "Settings" (via the gadget icon on the video player).
Even if the "Resume" feature is turned off, you can still check where you last left off on a video.
Click the icon that will show above the seek bar to start playing from your last session.
Thank you,
Niconico
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Starting December 8, 2016, niconico users will have access to the new Resume （continue）Feature for the HTML5 video watch page(β).
This feature will allow users to continue watching videos where they last left off.
Niconico PC version（available only on the HTML5 video watch page)
*This feature will be available on smartphones and for playback between smartphones and PCs at a later date.
Premium users
The resume feature allows you to continue watching videos where you last left off.
The following message will appear on the bottom left of the video player for re-watching videos from the place you last left off.
・Resume feature (or playback memory) will not be available for Flash video watch page.
・This feature will not be released for the Flash video watch page.
・Feature can only be used for videos within user Watch History.
・Resumed playback position may slightly change depending on your viewing environment.
Thank you,
Niconico