As mentioned I am not the codecs experts, but maybe you can try to post the output of this :-
$ mplayer -vc help |grep 264

On my computer, this is what I get :-

Code:
$ mplayer -vc help |grep 264
ffh264      ffmpeg    working   FFmpeg H.264  [h264]
ffh264vdpau ffmpeg    working   FFmpeg H.264 (VDPAU)  [h264_vdpau]
coreavcwindows dshow     working   CoreAVC H.264 for x86 - http://corecodec.org/  [CoreAVCDecoder.ax]
vssh264     dshow     working   VSS H.264 New  [vsshdsd.dll]
vssh264old  vfw       working   VSS H.264 Old  [vssh264.dll]
It seems I have both the ffmpeg h264 codec as well as vssh264 codec in the form of win32.dll.