Current questions and answers regarding the map editor.

First, you need to record the voiceover and save it in wav format, placing it in the Complete package (if it doesn't exist, you need to create it). Next, create a video, create a new sentence, and near the text, there's a parameter called sound. Click New and create it, then select the desired recording from the Complete folder.
Click OK.
Without closing the sound editing window, find the sound you created in the left tree, right-click, and select Export. At the bottom of the console, make sure there are no errors. Now, click OK everywhere, close it, and it should work.
(Compiled from AlekseyS's message and my addition)