}
		return sps
	}

	makeInput := func(format Format, size string, sps ...string) (out []byte) {
		// Write the initial GNU header.
		var blk block
		gnu := blk.toGNU()
		sparse := gnu.sparse()
		copy(gnu.realSize(), size)
		sps = populateSparseMap(sparse, sps)
		if format != FormatUnknown {
			blk.setFormat(format)
		}
		out = append(out, blk[:]...)