Did you have a crash as that is when output logs are generated, the metadata on yours says it was made 07/08/2016 so I'm assuming its a bit out of date and not relevant.

The Movies in ES2 Both the Main faction introductions and system colonization (and I assume the intro and victory videos too) have their audio played separately to the main game.

This can be seen by opening the volume mixer (One way to open it is Press Win+R and enter sndvol) and running the game, You should see 2 copies of “Endless space 2” in applications one is the all the game sound and the other is movie sounds. 

Make sure you can see 2 copies of "Endless space 2" if you can't check other audio devices in case its outputting the movies audio to the wrong place (if it is just disable the device its outputting to)

It also goes without saying that check that both copies are unmuted.

That’s my thoughts on the most likely causes of this, but if it is not try Verifying Game Cache (in case something went wrong with the movie files or FMOD. 

Do report back how it goes.

Only one copy of ES2 is in my sound mixer (checked and disabled other devices too). Validation was successful.

As for output log - yeah, it's not relevant. Shouldn't have attached it, my bad

EDIT:

Actually, there is a second copy of ES2 on a second device (which is my default communication device). However, that second ES2 doesn't play any sounds and yes, it's unmuted. And if I designate a single device as a regular default and communications default device, then there's only one copy of ES2 present in the mixer.

Yup, no drop down menu after disabling everything (except for one device ofc). Setup matches and when I play the movies outside of the game, they all have proper sound.

Another detail I noticed - very rarely, when colonising a planet, I can hear something for a split-second (usually I just hear nothing). However this sudden sound ends too abruptly so I can't even compare it to the movies and say if it matches or not (and no, it's not the usual es2 notification sound or anything of the sort).

I'll check that the next time I play.

Also, no, it used to be fine at some point. Specifically I remember watching Craver and Sophon intros back when they were the only intros in the game, probably in a private build since there was no Lumeris intro yet. Back then the intros worked fine. I'm not entirely sure when the issue started

EDIT: Fun fact - the planet destruction movies actually do have sound. I'll be honest, I completely forgot about it (since destroying planet is basically never worth your turn investment, except for some very rare situations in mp). The audio for this movie plays as part of the main game in the audio mixer (so only one copy of ES2, yours must be a unique case). But colonisation and intro movies are still soundless.

Good to know ^^ I have that issue too so it's nice to know I can work around it. I wouldn't ignore the bug report though. I'm sure other people are having this issue and I'm sure it's not intended.