diff --git a/hash.go b/hash.go
index 37ae981..c19276a 100644
--- a/hash.go
+++ b/hash.go
@@ -9,19 +9,14 @@ import (
 	"os"
 )
 
-// Hash creates a hash of the audio file data provided by the io.ReadSeeker
-// which ignores metadata (ID3, MP4) associated with the file.
+// Hash creates a hash of the audio file data provided by the io.ReadSeeker which metadata
+// (ID3, MP4) invariant.
 func Hash(r io.ReadSeeker) (string, error) {
 	b, err := readBytes(r, 11)
 	if err != nil {
 		return "", err
 	}
 
-	_, err = r.Seek(0, os.SEEK_SET)
-	if err != nil {
-		return "", err
-	}
-
 	if string(b[4:11]) == "ftypM4A" {
 		return HashAtoms(r)
 	}
@@ -42,6 +37,11 @@ func Hash(r io.ReadSeeker) (string, error) {
 
 // HashAll returns a hash of the entire content.
 func HashAll(r io.ReadSeeker) (string, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return "", fmt.Errorf("error seeking to 0: %v", err)
+	}
+
 	b, err := ioutil.ReadAll(r)
 	if err != nil {
 		return "", nil
@@ -49,7 +49,13 @@ func HashAll(r io.ReadSeeker) (string, error) {
 	return hash(b), nil
 }
 
+// HashAtoms constructs a hash of MP4 audio file data provided by the io.ReadSeeker which is metadata invariant.
 func HashAtoms(r io.ReadSeeker) (string, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return "", fmt.Errorf("error seeking to 0: %v", err)
+	}
+
 	for {
 		var size uint32
 		err := binary.Read(r, binary.BigEndian, &size)
@@ -99,10 +105,12 @@ func HashAtoms(r io.ReadSeeker) (string, error) {
 	}
 }
 
+// HashID3v1 constructs a hash of MP3 audio file data (assumed to have ID3v1 tags) provided by the
+// io.ReadSeeker which is metadata invariant.
 func HashID3v1(r io.ReadSeeker) (string, error) {
 	_, err := r.Seek(0, os.SEEK_SET)
 	if err != nil {
-		return "", err
+		return "", fmt.Errorf("error seeking to 0: %v", err)
 	}
 
 	b, err := ioutil.ReadAll(r)
@@ -116,7 +124,14 @@ func HashID3v1(r io.ReadSeeker) (string, error) {
 	return hash(b[:len(b)-128]), nil
 }
 
+// HashID3v2 constructs a hash of MP3 audio file data (assumed to have ID3v2 tags) provided by the
+// io.ReadSeeker which is metadata invariant.
 func HashID3v2(r io.ReadSeeker) (string, error) {
+	_, err := r.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return "", fmt.Errorf("error seeking to 0: %v", err)
+	}
+
 	h, err := readID3v2Header(r)
 	if err != nil {
 		return "", fmt.Errorf("error reading ID3v2 header: %v", err)
diff --git a/id3v1.go b/id3v1.go
index c37dfac..d054cbe 100644
--- a/id3v1.go
+++ b/id3v1.go
@@ -13,8 +13,8 @@ import (
 	"strings"
 )
 
-// ID3v1Genres is a list of genres as given in the ID3v1 specification.
-var ID3v1Genres = [...]string{
+// id3v1Genres is a list of genres as given in the ID3v1 specification.
+var id3v1Genres = [...]string{
 	"Blues", "Classic Rock", "Country", "Dance", "Disco", "Funk", "Grunge",
 	"Hip-Hop", "Jazz", "Metal", "New Age", "Oldies", "Other", "Pop", "R&B",
 	"Rap", "Reggae", "Rock", "Techno", "Industrial", "Alternative", "Ska",
@@ -95,8 +95,8 @@ func ReadID3v1Tags(r io.Reader) (Metadata, error) {
 	if err != nil {
 		return nil, err
 	}
-	if int(genreID[0]) < len(ID3v1Genres) {
-		genre = ID3v1Genres[int(genreID[0])]
+	if int(genreID[0]) < len(id3v1Genres) {
+		genre = id3v1Genres[int(genreID[0])]
 	}
 
 	m := make(map[string]interface{})