I don't know how internally Total War works under the hood but from what I have played and seen, I can say that they are not reflecting 1-1 sound of the battlefield - on purpose.
Currently, in Bannerlord each agent/soldier is broadcasting a sound event in 3D. Whether it's footsteps, hit, yell it's always like that. And this is a problem. Because when you have 1k agents on the battlefield sending events to your soundbus, it's creating issues for your soundplayer while merging and reflecting all of them. This is exactly the reason why we have this weird "sound channel" thingy in Performance options.
I think Total War is doing something similar to this,
- Based on unit count on the map, picking and perhaps merging sounds beforhand
- Based on the camera distance it's adjusting the sound intensity and playing that sound.
- Picking action cues, such as horseman dying or shield hits and emitting sound from that action while merged clash ambience is still playing
And that's why, for example, in the video, you put, at 02:08 to 02:12 you are not feeling any sound difference even though the location is completely different and the "actions" should be different as well. But it's simply continuing the same ambience because it's still the clash ambience between same units and same formations "horseman vs infantry". This gives a nice fake feeling of war ambience and that's the reason we like it ( I like it too btw even though I kinda ruined the magic right now I guess
)
Doing this on Bannerlord ain't easy - since each sound is 3D and you are actually a single man in that battle and you need that 3D knowledge to know if someone is running at you. This still can be tackled by removing distant sounds and replacing them with pre-assembled ambience sound. This isn't easy as I said but it will 100% increase the performance because the current approach is just sucking CPU. And it will definitely give a better sense of war and mayhem feeling to players.
Actually, I have an idea to try out but I hate Modding Tools and it appears to be the only way to add sounds right now so if you want to try something DM me Terco, we can discuss this