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mp4_decoder.go
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mp4_decoder.go
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package audiometa
import (
"bytes"
"encoding/binary"
"image"
"io"
"strconv"
"strings"
)
var atomTypes = map[int]string{
0: "implicit", // automatic based on atom name
1: "text",
13: "png",
14: "jpg",
21: "uint8",
}
// NB: atoms does not include "----", this is handled separately
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 struct {
data map[string]interface{}
}
func readFromMP4(r io.ReadSeeker) (metadataMP4, error) {
return readAtoms(r)
}
// ReadAtoms reads MP4 metadata atoms from the io.ReadSeeker into a Metadata, returning
// non-nil error if there was a problem.
func readAtoms(r io.ReadSeeker) (metadataMP4, error) {
m := metadataMP4{
data: make(map[string]interface{}),
}
err := m.readAtoms(r)
return m, err
}
func (m metadataMP4) readAtoms(r io.ReadSeeker) error {
for {
name, size, err := readAtomHeader(r)
if err != nil {
if err == io.EOF {
return nil
}
return err
}
switch name {
case "meta":
_, err := readBytes(r, 4)
if err != nil {
return err
}
fallthrough
case "moov", "udta", "ilst":
return m.readAtoms(r)
}
_, ok := atoms[name]
var data []string
if !ok {
_, err := r.Seek(int64(size-8), io.SeekCurrent)
if err != nil {
return err
}
continue
}
err = m.readAtomData(r, name, size-8, data)
if err != nil {
return err
}
}
}
func (m metadataMP4) readAtomData(r io.ReadSeeker, name string, size uint32, processedData []string) error {
var b []byte
var err error
var contentType string
if len(processedData) > 0 {
b = []byte(strings.Join(processedData, ";")) // add delimiter if multiple data fields
contentType = "text"
} else {
// read the data
b, err = readBytes(r, uint(size))
if err != nil {
return err
}
if len(b) < 8 {
return ErrMP4InvalidEncoding
}
// "data" + size (4 bytes each)
b = b[8:]
if len(b) < 4 {
return ErrMP4InvalidEncoding
}
class := getInt(b[1:4])
var ok bool
contentType, ok = atomTypes[class]
if !ok {
return ErrMP4InvalidCntntType
}
// 4: atom version (1 byte) + atom flags (3 bytes)
// 4: NULL (usually locale indicator)
if len(b) < 8 {
return ErrMP4InvalidEncoding
}
b = b[8:]
}
if name == "trkn" || name == "disk" {
if len(b) < 6 {
return ErrMP4InvalidEncoding
}
m.data[name] = int(b[3])
m.data[name+"_count"] = int(b[5])
return nil
}
if contentType == "implicit" {
if name == "covr" {
contentType = "png"
}
}
var data interface{}
switch contentType {
case "implicit":
if _, ok := atoms[name]; ok {
return ErrMP4InvalidCntntType
}
return nil
case "text":
data = string(b)
case "uint8":
if len(b) < 1 {
return ErrMP4InvalidEncoding
}
data = getInt(b[:1])
case "jpeg", "png":
if img, _, err := image.Decode(bytes.NewReader(b)); err == nil {
data = &img
}
}
m.data[name] = data
return nil
}
func readAtomHeader(r io.ReadSeeker) (name string, size uint32, err error) {
err = binary.Read(r, binary.BigEndian, &size)
if err != nil {
return
}
name, err = readString(r, 4)
return
}
func (m metadataMP4) getString(n []string) string {
for _, k := range n {
if x, ok := m.data[k]; ok {
return x.(string)
}
}
return ""
}
func (m metadataMP4) getInt(n []string) int {
for _, k := range n {
if x, ok := m.data[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) comment() string {
t, ok := m.data["\xa9cmt"]
if !ok {
return ""
}
return t.(string)
}
func (m metadataMP4) picture() *image.Image {
v, ok := m.data["covr"]
if !ok {
return nil
}
return v.(*image.Image)
}
func (m metadataMP4) tempo() int {
return m.getInt(atoms.name("tempo"))
}
func (m metadataMP4) encoder() string {
return m.getString(atoms.name("encoder"))
}
func (m metadataMP4) copyright() string {
return m.getString(atoms.name("copyright"))
}