132 lines
3.6 KiB
Go
132 lines
3.6 KiB
Go
// Copyright 2015, David Howden
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package tag provides MP3 (ID3: v1, 2.2, 2.3 and 2.4), MP4, FLAC and OGG metadata parsing and
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// artwork extraction.
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package tag
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import (
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"errors"
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"fmt"
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"io"
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"os"
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)
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// ErrNoTagsFound is the error returned by ReadFrom when the metadata format
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// cannot be identified.
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var ErrNoTagsFound = errors.New("no tags found")
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// ReadFrom parses audio file metadata tags (currently supports ID3v1,2.{2,3,4} and MP4).
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// This method attempts to determine the format of the data provided by the io.ReadSeeker,
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// and then chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as
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// appropriate. Returns non-nil error if the format of the given data could not be determined,
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// or if there was a problem parsing the data.
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func ReadFrom(r io.ReadSeeker) (Metadata, error) {
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b, err := readBytes(r, 11)
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if err != nil {
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return nil, err
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}
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_, err = r.Seek(-11, os.SEEK_CUR)
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if err != nil {
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return nil, fmt.Errorf("could not seek back to original position: %v", err)
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}
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switch {
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case string(b[0:4]) == "fLaC":
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return ReadFLACTags(r)
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case string(b[0:4]) == "OggS":
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return ReadOGGTags(r)
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case string(b[4:11]) == "ftypM4A":
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return ReadAtoms(r)
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case string(b[0:3]) == "ID3":
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return ReadID3v2Tags(r)
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}
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m, err := ReadID3v1Tags(r)
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if err != nil {
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if err == ErrNotID3v1 {
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err = ErrNoTagsFound
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}
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return nil, err
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}
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return m, nil
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}
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// Format is an enumeration of metadata types supported by this package.
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type Format string
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// Supported tag formats.
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const (
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ID3v1 Format = "ID3v1" // ID3v1 tag format.
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ID3v2_2 = "ID3v2.2" // ID3v2.2 tag format.
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ID3v2_3 = "ID3v2.3" // ID3v2.3 tag format (most common).
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ID3v2_4 = "ID3v2.4" // ID3v2.4 tag format.
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MP4 = "MP4" // MP4 tag (atom) format.
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VORBIS = "VORBIS" // Vorbis Comment tag format.
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)
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// FileType is an enumeration of the audio file types supported by this package, in particular
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// there are audio file types which share metadata formats, and this type is used to distinguish
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// between them.
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type FileType string
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// Supported file types.
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const (
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MP3 FileType = "MP3" // MP3 file
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AAC = "AAC" // M4A file (MP4)
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ALAC = "ALAC" // Apple Lossless file FIXME: actually detect this
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FLAC = "FLAC" // FLAC file
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OGG = "OGG" // OGG file
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)
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// Metadata is an interface which is used to describe metadata retrieved by this package.
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type Metadata interface {
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// Format returns the metadata Format used to encode the data.
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Format() Format
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// FileType returns the file type of the audio file.
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FileType() FileType
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// Title returns the title of the track.
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Title() string
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// Album returns the album name of the track.
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Album() string
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// Artist returns the artist name of the track.
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Artist() string
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// AlbumArtist returns the album artist name of the track.
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AlbumArtist() string
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// Composer returns the composer of the track.
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Composer() string
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// Year returns the year of the track.
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Year() int
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// Genre returns the genre of the track.
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Genre() string
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// Track returns the track number and total tracks, or zero values if unavailable.
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Track() (int, int)
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// Disc returns the disc number and total discs, or zero values if unavailable.
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Disc() (int, int)
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// Picture returns a picture, or nil if not available.
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Picture() *Picture
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// Lyrics returns the lyrics, or an empty string if unavailable.
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Lyrics() string
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// Raw returns the raw mapping of retrieved tag names and associated values.
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// NB: tag/atom names are not standardised between formats.
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Raw() map[string]interface{}
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}
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