I believe this refers to the possibilities when using x264 itself from the commandline, rather than when x264 is utilised by MEncoder or FFmpeg. Have a look at your own copy as follows:
Originally Posted by hissyfut
There has been a problem for some time with with gpac and x264 as can be seen in my own configuration above.
andrew@skamandros~$ x264 --help | head -n 11
x264 core:68 r1185 2956905
Syntax: x264 [options] -o outfile infile [widthxheight]
Infile can be raw YUV 4:2:0 (in which case resolution is required),
or YUV4MPEG 4:2:0 (*.y4m),
or AVI or Avisynth if compiled with AVIS support (no).
Outfile type is selected by filename:
.264 -> Raw bytestream
.mkv -> Matroska
.mp4 -> MP4 if compiled with GPAC support (no)