I think they all do. I use HDMI output, so I think there was a question of whether that didn't involve decoding but just passing it through to the TV, but I think when that question came up, I went to an AC3 channel and switched over to the A/V ports, and still got sound, so I'm pretty sure that it's decoding it. But I'm not positive. But it is certain that if you're using HDMI, that you'll hear sound.
It decodes AC-3 to the audio ports in Comonent mode, I know .
I've lost the sound on my HDMI port for some reason, so I'm back to using component cabling.