checking for FFMPEG... yes
checking for FFMPEG_POSTPROC... configure: error: Package requirements (libpostproc >= 51.11.0) were not met:

Requested 'libpostproc >= 51.11.0' but version of libpostproc is 51.1.0

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables FFMPEG_POSTPROC_CFLAGS
and FFMPEG_POSTPROC_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.