How to fix rendered cutscene aspect ratio in games?

[Mayh3M]

Some games such as GTA V and Dragon Age Inquisition support native 21:9 gameplay but render cutscenes in 16:9. I'm aware that Flawless Widescreen provides fixes for this issue in these particular games but I wanted to know HOW do modders find this fix in the first place?

I am trying to find a way to render cutscenes in 21:9 in Dragon Age Origins, which also supports 21:9 gameplay natively. There are no ini files that seem to determine cutscene aspect ratio so the solution seems to lie inside the games exe. Any tips on how I can begin finding a solution to this? Are there any specific hex codes to look for?