Build FFmpeg and Libav

details
use MinGW 64 with MSYS on Windows

pull repo

git clone https://github.com/FFmpeg/FFmpeg.git
cd FFmpeg
git checkout release/5.0

configure (windows)

./configure \
  --toolchain=msvc \
  --prefix="./ffmpeg_build" \
  --pkg-config-flags="--static" \
  --extra-cflags="-I./ffmpeg_build/include" \
  --extra-ldflags="-L./ffmpeg_build/lib" \
  --extra-libs=-lpthread \
  --extra-libs=-lm \
  --bindir="./bin" \
  --enable-small \
  --enable-static \
  --enable-version3 \
  --disable-runtime-cpudetect \
  --disable-programs \
  --disable-doc \
  --enable-vpx \
  --enable-encoder=apng

compile

make -j10
make install -j10

libvpx

git clone https://github.com/webmproject/libvpx.git

./configure \
  --target=x86_64-win64-vs17 \
  --disable-install-bins \
  --disable-examples \
  --disable-tools \
  --disable-docs \
  --enable-vp8 \
  --enbale-vp9 \
  --enable-webm-io \
  --enable-small

zlib

git clone https://github.com/madler/zlib.git
git checkout v1.2.12

mkdir build
cd build
cmake ..
cmake --build . --config Release