$ git clone -n https://src.fedoraproject.org/rpms/ffmpeg.git /var/lib/mock/f39-build-1650911-40484/root/chroot_tmpdir/scmroot/ffmpeg
Cloning into '/var/lib/mock/f39-build-1650911-40484/root/chroot_tmpdir/scmroot/ffmpeg'...
$ git fetch origin 648de9ce0667f5a151755e09f3545c920bf6522d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ffmpeg
 * [new ref]         648de9ce0667f5a151755e09f3545c920bf6522d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 648de9c Fix ffmpeg-allow-fdk-aac-free.patch to apply with git-am