Initial commit

mp4.go

@@ -0,0 +1,223 @@
+// Copyright 2015, David Howden
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tag
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"strconv"
+)
+
+var atomTypes = map[int]string{
+	0:  "uint8",
+	1:  "text",
+	13: "jpeg",
+	14: "png",
+	21: "uint8",
+}
+
+var atoms = atomNames(map[string]string{
+	"\xa9alb": "album",
+	"\xa9art": "artist",
+	"\xa9ART": "artist",
+	"aART":    "album_artist",
+	"\xa9day": "year",
+	"\xa9nam": "title",
+	"\xa9gen": "genre",
+	"trkn":    "track",
+	"\xa9wrt": "composer",
+	"\xa9too": "encoder",
+	"cprt":    "copyright",
+	"covr":    "picture",
+	"\xa9grp": "grouping",
+	"keyw":    "keyword",
+	"\xa9lyr": "lyrics",
+	"\xa9cmt": "comment",
+	"tmpo":    "tempo",
+	"cpil":    "compilation",
+	"disk":    "disc",
+})
+
+type atomNames map[string]string
+
+func (f atomNames) Name(n string) []string {
+	res := make([]string, 1)
+	for k, v := range f {
+		if v == n {
+			res = append(res, k)
+		}
+	}
+	return res
+}
+
+// metadataMP4 is the implementation of Metadata for MP4 tag (atom) data.
+type metadataMP4 map[string]interface{}
+
+// ReadAtoms reads MP4 metadata atoms from the reader into a Metadata, returning non-nil
+// error if there was a problem.
+func ReadAtoms(r io.Reader) (Metadata, error) {
+	m := make(metadataMP4)
+	err := m.readAtoms(r)
+	return m, err
+}
+
+func (m metadataMP4) readAtoms(r io.Reader) error {
+	for {
+		var size uint32
+		err := binary.Read(r, binary.BigEndian, &size)
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+
+		name, err := readString(r, 4)
+		if err != nil {
+			return err
+		}
+
+		switch name {
+		case "meta":
+			// next_item_id (int32)
+			_, err := readBytes(r, 4)
+			if err != nil {
+				return err
+			}
+			fallthrough
+		case "moov", "udta", "ilst":
+			return m.readAtoms(r)
+		case "free":
+			discardN(r, int64(size-8))
+			continue
+		case "mdat": // stop when we get to the data
+			return nil
+		}
+
+		b, err := readBytes(r, int(size-8))
+		if err != nil {
+			return err
+		}
+
+		_, ok := atoms[name]
+		if !ok {
+			continue
+		}
+
+		// 16: name + size + "data" + size (4 bytes each), have already read 8
+		b = b[8:]
+		class := getInt(b[1:4])
+		contentType, ok := atomTypes[class]
+		if !ok {
+			return fmt.Errorf("invalid content type: %v", class)
+		}
+
+		b = b[8:]
+		switch name {
+		case "trkn", "disk":
+			m[name] = int(b[3])
+			m[name+"_count"] = int(b[5])
+		default:
+			var data interface{}
+			// 4: atom version (1 byte) + atom flags (3 bytes)
+			// 4: NULL (usually locale indicator)
+			switch contentType {
+			case "text":
+				data = string(b)
+
+			case "uint8":
+				data = getInt(b[:1])
+
+			case "jpeg", "png":
+				data = &Picture{
+					Ext:      contentType,
+					MIMEType: "image/" + contentType,
+					Data:     b,
+				}
+			}
+			m[name] = data
+		}
+	}
+}
+
+func (metadataMP4) Format() Format { return MP4 }
+
+func (m metadataMP4) Raw() map[string]interface{} { return m }
+
+func (m metadataMP4) getString(n []string) string {
+	for _, k := range n {
+		if x, ok := m[k]; ok {
+			return x.(string)
+		}
+	}
+	return ""
+}
+
+func (m metadataMP4) getInt(n []string) int {
+	for _, k := range n {
+		if x, ok := m[k]; ok {
+			return x.(int)
+		}
+	}
+	return 0
+}
+
+func (m metadataMP4) Title() string {
+	return m.getString(atoms.Name("title"))
+}
+
+func (m metadataMP4) Artist() string {
+	return m.getString(atoms.Name("artist"))
+}
+
+func (m metadataMP4) Album() string {
+	return m.getString(atoms.Name("album"))
+}
+
+func (m metadataMP4) AlbumArtist() string {
+	return m.getString(atoms.Name("album_artist"))
+}
+
+func (m metadataMP4) Composer() string {
+	return m.getString(atoms.Name("composer"))
+}
+
+func (m metadataMP4) Genre() string {
+	return m.getString(atoms.Name("genre"))
+}
+
+func (m metadataMP4) Year() int {
+	date := m.getString(atoms.Name("year"))
+	if len(date) >= 4 {
+		year, _ := strconv.Atoi(date[:4])
+		return year
+	}
+	return 0
+}
+
+func (m metadataMP4) Track() (int, int) {
+	x := m.getInt([]string{"trkn"})
+	if n, ok := m["trkn_count"]; ok {
+		return x, n.(int)
+	}
+	return x, 0
+}
+
+func (m metadataMP4) Disc() (int, int) {
+	x := m.getInt([]string{"disk"})
+	if n, ok := m["disk_count"]; ok {
+		return x, n.(int)
+	}
+	return x, 0
+}
+
+func (m metadataMP4) Picture() *Picture {
+	v, ok := m["covr"]
+	if !ok {
+		return nil
+	}
+	return v.(*Picture)
+}