$ git clone -n https://src.fedoraproject.org/rpms/ffmpeg.git /var/lib/mock/f41-build-808106-145667/root/chroot_tmpdir/scmroot/ffmpeg
Cloning into '/var/lib/mock/f41-build-808106-145667/root/chroot_tmpdir/scmroot/ffmpeg'...
$ git fetch origin 16078d1d91a4ef0436f6821455e91b8ec6302902:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ffmpeg
 * [new ref]         16078d1d91a4ef0436f6821455e91b8ec6302902 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 16078d1 Rebuild for updated VapourSynth