ERROR: dav1d >= 0.2.1 not found using pkg-config - linux

Question

I am trying to build ffmpeg with dav1d. I've successfully built davit using the following commands:
git clone --depth=1 https://code.videolan.org/videolan/dav1d.git && \
cd dav1d && \
mkdir build && cd build && \
meson .. && \
ninja
After that, I am running a config command for the FFmpeg and get the error:
PKG_CONFIG_PATH="/app/ffmpeg_build/lib/pkgconfig" ./configure \
--prefix="/app/ffmpeg_build" \
--pkg-config-flags="--static" \
--extra-cflags="-I/app/ffmpeg_build/include" \
--extra-ldflags="-L/app/ffmpeg_build/lib" \
--extra-libs="-lpthread -lm" \
--bindir="/usr/local/bin" \
--enable-gpl \
--enable-libass \
--enable-libmp3lame \
--enable-libfreetype \
--enable-libopus \
--enable-libvorbis \
--enable-libx264 \
--enable-libdav1d \
--enable-nonfree
(All other libs are installed and FFmpeg configures and builds correctly with them if I omit --enable-libdav1d, but in case of the above command I get):
ERROR: dav1d >= 0.2.1 not found using pkg-config
I think the reason could be that meson puts bin files in the wrong directory. Could anyone please help?
P.S. I am using Ubuntu 18.04.
Example of build commands for the other libs:
git -C x264 pull 2> /dev/null || git clone --depth 1 https://code.videolan.org/videolan/x264.git && \
cd x264 && \
PKG_CONFIG_PATH="/app/ffmpeg_build/lib/pkgconfig" ./configure --prefix="/app/ffmpeg_build" --bindir="/usr/local/bin" --enable-static --enable-pic && \
make && \
make install

Answer 1

To pass the build you have to add ninja install:
git clone --depth=1 https://code.videolan.org/videolan/dav1d.git && \
cd dav1d && \
mkdir build && cd build && \
meson --bindir="/usr/local/bin" .. && \
ninja && \
ninja install
But this not enough, if you run FFmpeg after, you'll get:
ffmpeg: error while loading shared libraries: libdav1d.so.4: cannot open shared object file: No such file or directory
To fix this issue add /usr/local/lib/x86_64-linux-gnu to the LD_LIBRARY_PATH:
export LD_LIBRARY_PATH+=":/usr/local/lib/x86_64-linux-gnu"