I’m currently playing Halo 2 campaign on Legendary and any time someone speaks in a cutscene, there is no audio. Their lips just move but there is still music playing the background. This is true for both the Blur cutscenes and the classic ones.
Edit: I just started the Pillar of Autumn and the same thing happened for Halo CE, so I changed the post title.
Edit 2: I am making this edit for any future users that might find this thread. This was not a problem with the game, it was user error. I changed my audio in my Xbox settings from Stereo uncompressed to the 5.1 uncompressed, not really knowing what it meant. Apparently the way my monitor is set up, that didn’t jibe well.
So if you have done something similar in the settings and are experiencing no dialogue in Halo CE or 2, then just change it back to stereo uncompressed :).