$ git clone -n https://src.fedoraproject.org/rpms/ffmpeg.git /var/lib/mock/f42-build-side-1-3517014-46096/root/chroot_tmpdir/scmroot/ffmpeg
Cloning into '/var/lib/mock/f42-build-side-1-3517014-46096/root/chroot_tmpdir/scmroot/ffmpeg'...
$ git fetch origin d3e50323a84dc815e5bc3d9ac54d7f6fea42e2ca:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ffmpeg
 * [new ref]         d3e50323a84dc815e5bc3d9ac54d7f6fea42e2ca -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d3e5032 Add missing source files for riscv64