94 lines
2.6 KiB
Go
94 lines
2.6 KiB
Go
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// 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 basic MP3 (ID3v1,2.{2,3,4}) and MP4 metadata parsing.
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package tag
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import (
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"bytes"
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"errors"
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"io"
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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 reader, and then
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// chooses ReadAtoms (MP4), ReadID3v2Tags (ID3v2.{2,3,4}) or ReadID3v1Tags as appropriate.
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// Returns non-nil error if the format of the given data could not be determined, or if
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// there was a problem parsing the data.
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func ReadFrom(r io.Reader) (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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rr := io.MultiReader(bytes.NewReader(b), r)
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if string(b[4:11]) == "ftypM4A" {
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return ReadAtoms(rr)
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}
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if string(b[0:3]) == "ID3" {
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return ReadID3v2Tags(rr)
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}
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m, err := ReadID3v1Tags(rr)
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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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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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)
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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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// 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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// 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 avilable.
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Picture() *Picture
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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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