$ git clone -n https://src.fedoraproject.org/rpms/ffmpeg.git /var/lib/mock/f39-build-1626252-39260/root/chroot_tmpdir/scmroot/ffmpeg
Cloning into '/var/lib/mock/f39-build-1626252-39260/root/chroot_tmpdir/scmroot/ffmpeg'...
$ git fetch origin 5c9c69c3c1ab705d086d53bb8c38ccd6fbd52c6e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ffmpeg
 * [new ref]         5c9c69c3c1ab705d086d53bb8c38ccd6fbd52c6e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5c9c69c Backport upstream patch to fix segfault when passing non-existent filter