MediaOverlay is not work

[lgst]

I can't find enable MediaOverlay's code in the SDKLauncher-Android, how enable it?
Where there are API Document，SDKLauncher-Android too simple，but I couldn't find the document！
Thank you!

[danielweck]

Play/Pause/Previous/Next buttons for EPUB3 MediaOverlays (synchronized highlighted text/audio "talking books") are available in the user interface when a publication is successfully loaded with the required MO metadata, SMIL files, etc.

See mIsMoAvailable, mIsMoPlaying, mo_previous, mo_next, mo_play, mo_pause (etc.) in:
https://github.com/readium/SDKLauncher-Android/blob/develop/SDKLauncher-Android/app/src/main/java/org/readium/sdk/android/launcher/WebViewActivity.java#L784

Otherwise, maybe playback fails for another reason, and I wonder if this is a related issue: readium/readium-js-viewer#681