I recently installed the 64-bit Media Player Classic – Home Cinema (MPC-HC), version 188.8.131.5266 (744df1c) on a new Windows 8 computer. When I tried to play back H.264 content that included subtitles, the video stuttered terribly. Scenes without subtitles played fine. Turning off subtitles was not an acceptable option.
After clicking around in the settings to no avail, I looked online and stumbled onto this Subtitles FAQ at Codec Guide. The answer was to uncheck Allow animation when buffering in MPC-HC’s subtitles options. Thanks Codec Guide!