cmd/torrent/piece-length.go => metainfo/piece-length.go | 18 +++++++++---------
 cmd/torrent/serve.go                                    |  2 +-
 metainfo/info.go                                        |  3 +++
 metainfo/metainfo.go                                    |  2 --

diff --git a/cmd/torrent/piece-length.go b/metainfo/piece-length.go
rename from cmd/torrent/piece-length.go
rename to metainfo/piece-length.go
index b6574fd36f469327f7243d0675368dba8bd68f8e..9835dc5b2fbeae4c287abe5803fccd5b932ba8f3 100644
--- a/cmd/torrent/piece-length.go
+++ b/metainfo/piece-length.go
@@ -28,24 +28,24 @@ // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-package main
+package metainfo
 
 // For more context on why these numbers, see http://wiki.vuze.com/w/Torrent_Piece_Size
-const MinimumPieceLength = 16 * 1024
-const TargetPieceCountLog2 = 10
-const TargetPieceCountMin = 1 << TargetPieceCountLog2
+const minimumPieceLength = 16 * 1024
+const targetPieceCountLog2 = 10
+const targetPieceCountMin = 1 << targetPieceCountLog2
 
-// Target piece count should be < TargetPieceCountMax
-const TargetPieceCountMax = TargetPieceCountMin << 1
+// Target piece count should be < targetPieceCountMax
+const targetPieceCountMax = targetPieceCountMin << 1
 
 // Choose a good piecelength.
-func choosePieceLength(totalLength int64) (pieceLength int64) {
+func ChoosePieceLength(totalLength int64) (pieceLength int64) {
 	// Must be a power of 2.
 	// Must be a multiple of 16KB
 	// Prefer to provide around 1024..2048 pieces.
-	pieceLength = MinimumPieceLength
+	pieceLength = minimumPieceLength
 	pieces := totalLength / pieceLength
-	for pieces >= TargetPieceCountMax {
+	for pieces >= targetPieceCountMax {
 		pieceLength <<= 1
 		pieces >>= 1
 	}
diff --git a/cmd/torrent/serve.go b/cmd/torrent/serve.go
index 7915ddd91a33779f963ea355a3d17336a867bf7a..b32f245b089dc83813e7d5de8c56ba7e235eb0c9 100644
--- a/cmd/torrent/serve.go
+++ b/cmd/torrent/serve.go
@@ -31,7 +31,7 @@ 		totalLength, err := totalLength(filePath)
 		if err != nil {
 			return fmt.Errorf("calculating total length of %q: %v", filePath, err)
 		}
-		pieceLength := choosePieceLength(totalLength)
+		pieceLength := metainfo.ChoosePieceLength(totalLength)
 		info := metainfo.Info{
 			PieceLength: pieceLength,
 		}
diff --git a/metainfo/info.go b/metainfo/info.go
index 1b7944738081d823f1e4836715b898b9f2fa486d..bab08af945a6045582732339b9ebc27459a07c6b 100644
--- a/metainfo/info.go
+++ b/metainfo/info.go
@@ -74,6 +74,9 @@ 	}
 	slices.Sort(info.Files, func(l, r FileInfo) bool {
 		return strings.Join(l.Path, "/") < strings.Join(r.Path, "/")
 	})
+	if info.PieceLength == 0 {
+		info.PieceLength = ChoosePieceLength(info.TotalLength())
+	}
 	err = info.GeneratePieces(func(fi FileInfo) (io.ReadCloser, error) {
 		return os.Open(filepath.Join(root, strings.Join(fi.Path, string(filepath.Separator))))
 	})
diff --git a/metainfo/metainfo.go b/metainfo/metainfo.go
index 7ffa6d5b8f9b6e7637dcd7a4115d562f2c0a318e..cd787260c150e972b8987713b65904a7f30c766b 100644
--- a/metainfo/metainfo.go
+++ b/metainfo/metainfo.go
@@ -62,10 +62,8 @@ }
 
 // Set good default values in preparation for creating a new MetaInfo file.
 func (mi *MetaInfo) SetDefaults() {
-	mi.Comment = ""
 	mi.CreatedBy = "github.com/anacrolix/torrent"
 	mi.CreationDate = time.Now().Unix()
-	// mi.Info.PieceLength = 256 * 1024
 }
 
 // Creates a Magnet from a MetaInfo. Optional infohash and parsed info can be provided.