diff --git a/build.sh b/build.sh
index 802a609..ef82b48 100755
--- a/build.sh
+++ b/build.sh
@@ -50,6 +50,11 @@ rm -f "$TESTFILE"
 rm -rf ffbuild
 mkdir ffbuild
 
+FFMPEG_REPO="${FFMPEG_REPO:-https://github.com/FFmpeg/FFmpeg.git}"
+FFMPEG_REPO="${FFMPEG_REPO_OVERRIDE:-$FFMPEG_REPO}"
+GIT_BRANCH="${GIT_BRANCH:-master}"
+GIT_BRANCH="${GIT_BRANCH_OVERRIDE:-$GIT_BRANCH}"
+
 BUILD_SCRIPT="$(mktemp)"
 trap "rm -f -- '$BUILD_SCRIPT'" EXIT
 
@@ -58,9 +63,8 @@ cat <<EOF >"$BUILD_SCRIPT"
     cd /ffbuild
     rm -rf ffmpeg prefix
 
-    git clone https://github.com/FFmpeg/FFmpeg.git ffmpeg
+    git clone --filter=blob:none --branch='$GIT_BRANCH' '$FFMPEG_REPO' ffmpeg
     cd ffmpeg
-    git checkout $GIT_BRANCH
 
     ./configure --prefix=/ffbuild/prefix --pkg-config-flags="--static" \$FFBUILD_TARGET_FLAGS $FF_CONFIGURE \
         --extra-cflags='$FF_CFLAGS' --extra-cxxflags='$FF_CXXFLAGS' \