./configure --enable-x264

....
ffmpeg/libavcodec/libavcodec.a(libx264.o): In function `X264_frame':
libx264.c:(.text+0x16a): undefined reference to `x264_picture_init'
libx264.c:(.text+0x21b): undefined reference to `x264_encoder_reconfig'
libx264.c:(.text+0x246): undefined reference to `x264_encoder_reconfig'
libx264.c:(.text+0x268): undefined reference to `x264_encoder_encode'
libx264.c:(.text+0x30d): undefined reference to `x264_encoder_encode'
libx264.c:(.text+0x354): undefined reference to `x264_encoder_delayed_frames'
ffmpeg/libavcodec/libavcodec.a(libx264.o): In function `X264_close':
libx264.c:(.text.unlikely+0x2a): undefined reference to `x264_encoder_close'
ffmpeg/libavcodec/libavcodec.a(libx264.o): In function `X264_init':
libx264.c:(.text.unlikely+0x67): undefined reference to `x264_param_default'
libx264.c:(.text.unlikely+0x494): undefined reference to `x264_param_default_preset'
libx264.c:(.text.unlikely+0x4db): undefined reference to `x264_param_parse'
libx264.c:(.text.unlikely+0x5d9): undefined reference to `x264_param_parse'
libx264.c:(.text.unlikely+0x667): undefined reference to `x264_param_parse'
libx264.c:(.text.unlikely+0x6d9): undefined reference to `x264_param_parse'
libx264.c:(.text.unlikely+0x754): undefined reference to `x264_param_apply_fastfirstpass'
libx264.c:(.text.unlikely+0x76b): undefined reference to `x264_param_apply_profile'
libx264.c:(.text.unlikely+0x888): undefined reference to `x264_encoder_open_116'
libx264.c:(.text.unlikely+0x8cb): undefined reference to `x264_encoder_headers'
collect2: ld returned 1 exit status
make: *** [mplayer] Error 1