A forum post to Chinese-language site weiphone.com (Translated Link) indicates that the iPhone 3GS is capable of playing back both 720p and 1080p video encoded in H.264 through the built-in video player, suggesting that Apple is currently placing arbitrary limits on the device, either to preserve battery life or keep its functionality more consistent with that of prior iPhone OS devices. Using the free document storage and viewing application FileAid,…