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tag.go
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// 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 provides MP3 (ID3: v1, 2.2, 2.3 and 2.4), MP4, FLAC and OGG metadata detection,
// parsing and artwork extraction.
//
// Detect and parse tag metadata from an io.ReadSeeker (i.e. an *os.File):
// m, err := tag.ReadFrom(f)
// if err != nil {
// log.Fatal(err)
// }
// log.Print(m.Format()) // The detected format.
// log.Print(m.Title()) // The title of the track (see Metadata interface for more details).
package tag
import (
"errors"
"fmt"
"io"
)
// ErrNoTagsFound is the error returned by ReadFrom when the metadata format
// cannot be identified.
var ErrNoTagsFound = errors.New("no tags found")
// ReadFrom detects and parses audio file metadata tags (currently supports ID3v1,2.{2,3,4}, MP4, FLAC/OGG).
// Returns non-nil error if the format of the given data could not be determined, or if there was a problem
// parsing the data.
func ReadFrom(r io.ReadSeeker) (Metadata, error) {
b, err := readBytes(r, 11)
if err != nil {
return nil, err
}
_, err = r.Seek(-11, io.SeekCurrent)
if err != nil {
return nil, fmt.Errorf("could not seek back to original position: %v", err)
}
switch {
case string(b[0:4]) == "fLaC":
return ReadFLACTags(r)
case string(b[0:4]) == "OggS":
return ReadOGGTags(r)
case string(b[4:8]) == "ftyp":
return ReadAtoms(r)
case string(b[0:3]) == "ID3":
return ReadID3v2Tags(r)
case string(b[0:4]) == "DSD ":
return ReadDSFTags(r)
}
m, err := ReadID3v1Tags(r)
if err != nil {
if err == ErrNotID3v1 {
err = ErrNoTagsFound
}
return nil, err
}
return m, nil
}
// Format is an enumeration of metadata types supported by this package.
type Format string
// Supported tag formats.
const (
UnknownFormat Format = "" // Unknown Format.
ID3v1 Format = "ID3v1" // ID3v1 tag format.
ID3v2_2 Format = "ID3v2.2" // ID3v2.2 tag format.
ID3v2_3 Format = "ID3v2.3" // ID3v2.3 tag format (most common).
ID3v2_4 Format = "ID3v2.4" // ID3v2.4 tag format.
MP4 Format = "MP4" // MP4 tag (atom) format (see http://www.ftyps.com/ for a full file type list)
VORBIS Format = "VORBIS" // Vorbis Comment tag format.
)
// FileType is an enumeration of the audio file types supported by this package, in particular
// there are audio file types which share metadata formats, and this type is used to distinguish
// between them.
type FileType string
// Supported file types.
const (
UnknownFileType FileType = "" // Unknown FileType.
MP3 FileType = "MP3" // MP3 file
M4A FileType = "M4A" // M4A file Apple iTunes (ACC) Audio
M4B FileType = "M4B" // M4A file Apple iTunes (ACC) Audio Book
M4P FileType = "M4P" // M4A file Apple iTunes (ACC) AES Protected Audio
ALAC FileType = "ALAC" // Apple Lossless file FIXME: actually detect this
FLAC FileType = "FLAC" // FLAC file
OGG FileType = "OGG" // OGG file
DSF FileType = "DSF" // DSF file DSD Sony format see https://dsd-guide.com/sites/default/files/white-papers/DSFFileFormatSpec_E.pdf
)
// Metadata is an interface which is used to describe metadata retrieved by this package.
type Metadata interface {
// Format returns the metadata Format used to encode the data.
Format() Format
// FileType returns the file type of the audio file.
FileType() FileType
// Title returns the title of the track.
Title() string
// Album returns the album name of the track.
Album() string
// Artist returns the artist name of the track.
Artist() string
// AlbumArtist returns the album artist name of the track.
AlbumArtist() string
// Composer returns the composer of the track.
Composer() string
// Year returns the year of the track.
Year() int
// Genre returns the genre of the track.
Genre() string
// Track returns the track number and total tracks, or zero values if unavailable.
Track() (int, int)
// Disc returns the disc number and total discs, or zero values if unavailable.
Disc() (int, int)
// Picture returns a picture, or nil if not available.
Picture() *Picture
// Lyrics returns the lyrics, or an empty string if unavailable.
Lyrics() string
// Comment returns the comment, or an empty string if unavailable.
Comment() string
// Raw returns the raw mapping of retrieved tag names and associated values.
// NB: tag/atom names are not standardised between formats.
Raw() map[string]interface{}
}