emms package

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+;;; emms-info-native.el --- Native Emacs Lisp info method for EMMS -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2020-2023 Free Software Foundation, Inc.
+
+;; Author: Petteri Hintsanen <[email protected]>
+
+;; This file is part of EMMS.
+
+;; EMMS is free software; you can redistribute it and/or modify it
+;; under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3, or (at your option)
+;; any later version.
+
+;; EMMS is distributed in the hope that it will be useful, but WITHOUT
+;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+;; or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+;; License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with EMMS; see the file COPYING. If not, write to the Free
+;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+;; MA 02110-1301, USA.
+
+;;; Commentary:
+
+;; This file provides a native emms-info-method for EMMS.  Here
+;; "native" means a pure Emacs Lisp implementation instead of one
+;; relying on external tools or libraries like `emms-info-ogginfo' or
+;; `emms-info-libtag'.
+;;
+;; To use this method, add `emms-info-native' to
+;; `emms-info-functions'.
+;;
+;; The following file formats are supported:
+;;
+;; - Vorbis: Ogg Vorbis I Profile, filename extension `.ogg',
+;;   elementary streams only.  Based on xiph.org's Vorbis I
+;;   specification, see URL
+;;   `https://xiph.org/vorbis/doc/Vorbis_I_spec.html'.
+;;
+;; - Opus: Ogg Opus profile, filename extension `.opus', elementary
+;;   streams only.  Based on RFC 7845, see URL
+;;   `https://tools.ietf.org/html/rfc7845.html'.
+;;
+;; - FLAC streams in native encapsulation format, filename extension
+;;   `.flac'.  Based on xiph.org's FLAC format specification, see URL
+;;   `https://xiph.org/flac/format.html'.
+;;
+;; - MP3 files with extension `.mp3' and id3v2 tags.  All id3v2
+;;   versions should work, but many features like CRC, compression and
+;;   encryption are not supported.  Based on id3v2 Informal Standards,
+;;   see URL `https://id3.org'.
+;;
+;; - SPC files with extension `.spc' and id666 tags.  This is an audio
+;;   file based on a memory dump from an SPC700, a special audio chip
+;;   found within Super Nintendos.
+;;
+;; Format detection is based solely on filename extension, which is
+;; matched case-insensitively.
+
+;;; Code:
+
+(require 'bindat)
+(require 'cl-lib)
+(require 'emms-info)
+(require 'emms-info-spc)
+(require 'seq)
+(require 'subr-x)
+
+(defconst emms-info-native--max-peek-size (* 2048 1024)
+  "Maximum buffer size for metadata decoding.
+Functions called by `emms-info-native' read certain amounts of
+data into a temporary buffer while decoding metadata.  This
+variable controls the maximum size of that buffer: if more than
+`emms-info-native--max-peek-size' bytes are needed, an error is
+signaled.
+
+Technically metadata blocks can have almost arbitrary lengths,
+but in practice processing must be constrained to prevent memory
+exhaustion in case of garbled or malicious inputs.")
+
+(defvar emms-info-native--opus-channel-count 0
+  "Last decoded Opus channel count.
+This is a kludge; it is needed because bindat spec cannot refer
+outside itself.")
+
+(defvar emms-info-native--id3v2-version 0
+  "Last decoded id3v2 version.
+This is a kludge; it is needed because bindat spec cannot refer
+outside itself.")
+
+;;;; Vorbis code
+
+(defconst emms-info-native--max-num-vorbis-comments 1024
+  "Maximum number of Vorbis comment fields in a stream.
+Technically a single Vorbis stream may have up to 2^32 comments,
+but in practice processing must be constrained to prevent memory
+exhaustion in case of garbled or malicious inputs.
+
+This limit is used with Opus and FLAC streams as well, since
+their comments have almost the same format as Vorbis.")
+
+(defconst emms-info-native--max-vorbis-comment-size (* 64 1024)
+  "Maximum length for a single Vorbis comment field.
+Technically a single Vorbis comment may have a length up to 2^32
+bytes, but in practice processing must be constrained to prevent
+memory exhaustion in case of garbled or malicious inputs.
+
+This limit is used with Opus and FLAC streams as well, since
+their comments have almost the same format as Vorbis.")
+
+(defconst emms-info-native--max-vorbis-vendor-length 1024
+  "Maximum length of Vorbis vendor string.
+Technically a vendor string can be up to 2^32 bytes long, but in
+practice processing must be constrained to prevent memory
+exhaustion in case of garbled or malicious inputs.
+
+This limit is used with Opus and FLAC streams as well, since
+their comments have almost the same format as Vorbis.")
+
+(defconst emms-info-native--accepted-vorbis-fields
+  '("album"
+    "albumartist"
+    "albumartistsort"
+    "albumsort"
+    "artist"
+    "artistsort"
+    "composer"
+    "composersort"
+    "date"
+    "discnumber"
+    "genre"
+    "label"
+    "originaldate"
+    "originalyear"
+    "performer"
+    "title"
+    "titlesort"
+    "tracknumber"
+    "year")
+  "EMMS info fields that are extracted from Vorbis comments.")
+
+(defconst emms-info-native--vorbis-headers-bindat-spec
+  '((identification-header struct emms-info-native--vorbis-identification-header-bindat-spec)
+    (comment-header struct emms-info-native--vorbis-comment-header-bindat-spec))
+  "Specification for first two Vorbis header packets.
+They are always an identification header followed by a comment
+header.")
+
+(defconst emms-info-native--vorbis-identification-header-bindat-spec
+  '((packet-type u8)
+    (eval (unless (= last 1)
+            (error "Vorbis header type mismatch: expected 1, got %s"
+                   last)))
+    (vorbis vec 6)
+    (eval (unless (equal last emms-info-native--vorbis-magic-array)
+            (error "Vorbis framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--vorbis-magic-array
+                   last)))
+    (vorbis-version u32r)
+    (eval (unless (= last 0)
+            (error "Vorbis version mismatch: expected 0, got %s"
+                   last)))
+    (audio-channels u8)
+    (audio-sample-rate u32r)
+    (bitrate-maximum u32r)
+    (bitrate-nominal u32r)
+    (bitrate-minimum u32r)
+    (blocksize u8)
+    (framing-flag u8)
+    (eval (unless (= last 1))
+          (error "Vorbis framing bit mismatch: expected 1, got %s"
+                 last)))
+  "Vorbis identification header specification.")
+
+(defconst emms-info-native--vorbis-magic-array
+  [118 111 114 98 105 115]
+  "Header packet magic pattern `vorbis'.")
+
+(defconst emms-info-native--vorbis-comment-header-bindat-spec
+  '((packet-type u8)
+    (eval (unless (= last 3)
+            (error "Vorbis header type mismatch: expected 3, got %s"
+                   last)))
+    (vorbis vec 6)
+    (eval (unless (equal last emms-info-native--vorbis-magic-array)
+            (error "Vorbis framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--vorbis-magic-array
+                   last)))
+    (vendor-length u32r)
+    (eval (when (> last emms-info-native--max-vorbis-vendor-length)
+            (error "Vorbis vendor length %s is too long" last)))
+    (vendor-string vec (vendor-length))
+    (user-comments-list-length u32r)
+    (eval (when (> last emms-info-native--max-num-vorbis-comments)
+            (error "Vorbis user comment list length %s is too long"
+                   last)))
+    (user-comments repeat
+                   (user-comments-list-length)
+                   (struct emms-info-native--vorbis-comment-field-bindat-spec))
+    (framing-bit u8)
+    (eval (unless (= last 1))
+          (error "Vorbis framing bit mismatch: expected 1, got %s"
+                 last)))
+  "Vorbis comment header specification.")
+
+(defconst emms-info-native--vorbis-comment-field-bindat-spec
+  '((length u32r)
+    (eval (when (> last emms-info-native--max-vorbis-comment-size)
+            (error "Vorbis comment length %s is too long" last)))
+    (user-comment vec (length)))
+  "Vorbis comment field specification.")
+
+(defun emms-info-native--extract-vorbis-comments (user-comments)
+  "Return a decoded list of comments from USER-COMMENTS.
+USER-COMMENTS should be a list of Vorbis comments according to
+`user-comments' field in
+`emms-info-native--vorbis-comment-header-bindat-spec',
+`emms-info-native--opus-comment-header-bindat-spec' or
+`emms-info-native--flac-comment-block-bindat-spec'.
+
+Return comments in a list of (FIELD . VALUE) cons cells.  Only
+FIELDs that are listed in
+`emms-info-native--accepted-vorbis-fields' are returned."
+  (let (comments)
+    (dolist (user-comment user-comments)
+      (let* ((comment (cdr (assoc 'user-comment user-comment)))
+             (pair (emms-info-native--split-vorbis-comment comment)))
+        (push pair comments)))
+    (seq-filter (lambda (elt)
+                  (member (car elt)
+                          emms-info-native--accepted-vorbis-fields))
+                comments)))
+
+(defun emms-info-native--split-vorbis-comment (comment)
+  "Split Vorbis comment to a field-value pair.
+Vorbis comments are of form `FIELD=VALUE'.  FIELD is a
+case-insensitive field name with a restricted set of ASCII
+characters.  VALUE is an arbitrary UTF-8 encoded octet stream.
+
+Return a cons cell (FIELD . VALUE), where FIELD is converted to
+lower case and VALUE is the decoded value."
+  (let ((comment-string (decode-coding-string (mapconcat
+                                               #'byte-to-string
+                                               comment
+                                               nil)
+                                              'utf-8)))
+    (when (string-match "^\\(.+?\\)=\\(.+?\\)$" comment-string)
+      (cons (downcase (match-string 1 comment-string))
+            (match-string 2 comment-string)))))
+
+;;;; Opus code
+
+(defconst emms-info-native--opus-headers-bindat-spec
+  '((identification-header struct emms-info-native--opus-identification-header-bindat-spec)
+    (comment-header struct emms-info-native--opus-comment-header-bindat-spec))
+  "Specification for two first Opus header packets.
+They are always an identification header followed by a comment
+header.")
+
+(defconst emms-info-native--opus-identification-header-bindat-spec
+  '((opus-head vec 8)
+    (eval (unless (equal last emms-info-native--opus-head-magic-array)
+            (error "Opus framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--opus-head-magic-array
+                   last)))
+    (opus-version u8)
+    (eval (unless (< last 16)
+            (error "Opus version mismatch: expected < 16, got %s"
+                   last)))
+    (channel-count u8)
+    (eval (setq emms-info-native--opus-channel-count last))
+    (pre-skip u16r)
+    (sample-rate u32r)
+    (output-gain u16r)
+    (channel-mapping-family u8)
+    (union (channel-mapping-family)
+           (0 nil)
+           (t (struct emms-info-native--opus-channel-mapping-table))))
+  "Opus identification header specification.")
+
+(defconst emms-info-native--opus-head-magic-array
+  [79 112 117 115 72 101 97 100]
+  "Opus identification header magic pattern `OpusHead'.")
+
+(defconst emms-info-native--opus-channel-mapping-table
+  '((stream-count u8)
+    (coupled-count u8)
+    (channel-mapping vec (eval emms-info-native--opus-channel-count)))
+  "Opus channel mapping table specification.")
+
+(defconst emms-info-native--opus-comment-header-bindat-spec
+  '((opus-tags vec 8)
+    (eval (unless (equal last emms-info-native--opus-tags-magic-array)
+            (error "Opus framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--opus-tags-magic-array
+                   last)))
+    (vendor-length u32r)
+    (eval (when (> last emms-info-native--max-vorbis-vendor-length)
+            (error "Opus vendor length %s is too long" last)))
+    (vendor-string vec (vendor-length))
+    (user-comments-list-length u32r)
+    (eval (when (> last emms-info-native--max-num-vorbis-comments)
+            (error "Opus user comment list length %s is too long"
+                   last)))
+    (user-comments repeat
+                   (user-comments-list-length)
+                   (struct emms-info-native--vorbis-comment-field-bindat-spec)))
+  "Opus comment header specification.")
+
+(defconst emms-info-native--opus-tags-magic-array
+  [79 112 117 115 84 97 103 115]
+  "Opus comment header magic pattern `OpusTags'.")
+
+;;;; Ogg code
+
+(defconst emms-info-native--ogg-page-size 65307
+  "Maximum size for a single Ogg container page.")
+
+(defconst emms-info-native--ogg-page-bindat-spec
+  '((capture-pattern vec 4)
+    (eval (unless (equal last emms-info-native--ogg-magic-array)
+            (error "Ogg framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--ogg-magic-array
+                   last)))
+    (stream-structure-version u8)
+    (eval (unless (= last 0)
+            (error ("Ogg version mismatch: expected 0, got %s")
+                   last)))
+    (header-type-flag u8)
+    (granule-position vec 8)
+    (stream-serial-number vec 4)
+    (page-sequence-no vec 4)
+    (page-checksum vec 4)
+    (page-segments u8)
+    (segment-table vec (page-segments))
+    (payload vec (eval (seq-reduce #'+ last 0))))
+  "Ogg page structure specification.")
+
+(defconst emms-info-native--ogg-magic-array
+  [79 103 103 83]
+  "Ogg format magic capture pattern `OggS'.")
+
+(defun emms-info-native--decode-ogg-comments (filename stream-type)
+  "Read and decode comments from Ogg file FILENAME.
+The file is assumed to contain a single stream of type
+STREAM-TYPE, which must either `vorbis' or `opus'.
+
+Return comments in a list of (FIELD . VALUE) cons cells.  See
+`emms-info-native--split-vorbis-comment' for details."
+  (let* ((packets (emms-info-native--decode-ogg-packets filename 2))
+         (headers (emms-info-native--decode-ogg-headers packets
+                                                        stream-type))
+         (comments (bindat-get-field headers
+                                     'comment-header
+                                     'user-comments)))
+    (emms-info-native--extract-vorbis-comments comments)))
+
+(defun emms-info-native--decode-ogg-packets (filename packets)
+  "Read and decode packets from Ogg file FILENAME.
+Read in data from the start of FILENAME, remove Ogg packet
+frames, and concatenate payloads until at least PACKETS number of
+packets have been decoded.  Return the decoded packets in a
+vector, concatenated.
+
+Data is read in `emms-info-native--ogg-page-size' chunks.  If the
+total length of concatenated packets becomes greater than
+`emms-info-native--max-peek-size', an error is signaled.
+
+Only elementary streams are supported, that is, FILENAME should
+contain only a single logical stream.  Note that this assumption
+is not verified: with non-elementary streams packets from
+different streams will be mixed together without an error."
+  (let ((num-packets 0)
+        (offset 0)
+        (stream (vector)))
+    (while (< num-packets packets)
+      (let ((page (emms-info-native--decode-ogg-page filename
+                                                     offset)))
+        (cl-incf num-packets (or (plist-get page :num-packets) 0))
+        (cl-incf offset (plist-get page :num-bytes))
+        (setq stream (vconcat stream (plist-get page :stream)))
+        (when (> (length stream) emms-info-native--max-peek-size)
+          (error "Ogg payload is too large"))))
+    stream))
+
+(defun emms-info-native--decode-ogg-page (filename offset)
+  "Read and decode a single Ogg page from FILENAME.
+Starting reading data from byte offset OFFSET.
+
+Return a plist (:num-packets N :num-bytes B :stream S), where N
+is the number of packets in the page, B is the size of the page
+in bytes, and S is the unframed logical bitstream in a vector.
+Note that N can be zero."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (insert-file-contents-literally filename
+                                    nil
+                                    offset
+                                    (+ offset
+                                       emms-info-native--ogg-page-size))
+    (let* ((page (bindat-unpack emms-info-native--ogg-page-bindat-spec
+                                (buffer-string)))
+           (num-packets (emms-info-native--num-of-packets page))
+           (num-bytes (bindat-length emms-info-native--ogg-page-bindat-spec
+                                     page))
+           (stream (bindat-get-field page 'payload)))
+      (list :num-packets num-packets
+            :num-bytes num-bytes
+            :stream stream))))
+
+(defun emms-info-native--num-of-packets (page)
+  "Return the number of packets in Ogg page PAGE.
+PAGE must correspond to
+`emms-info-native--ogg-page-bindat-spec'."
+  ;; Every element that is less than 255 in the segment table
+  ;; represents a packet boundary.
+  (length (seq-filter (lambda (elt) (< elt 255))
+                      (bindat-get-field page 'segment-table))))
+
+(defun emms-info-native--decode-ogg-headers (packets stream-type)
+  "Decode first two stream headers from PACKETS for STREAM-TYPE.
+STREAM-TYPE must be either `vorbis' or `opus'.
+
+Return a structure that corresponds to either
+`emms-info-native--opus-headers-bindat-spec' or
+`emms-info-native--vorbis-headers-bindat-spec'."
+  (cond ((eq stream-type 'vorbis)
+         (bindat-unpack emms-info-native--vorbis-headers-bindat-spec
+                        packets))
+        ((eq stream-type 'opus)
+         (let (emms-info-native--opus-channel-count)
+           (bindat-unpack emms-info-native--opus-headers-bindat-spec
+                          packets)))
+        (t (error "Unknown stream type %s" stream-type))))
+
+;;;; FLAC code
+
+(defconst emms-info-native--flac-metadata-block-header-bindat-spec
+  '((flags u8)
+    (length u24)
+    (eval (when (or (> last emms-info-native--max-peek-size)
+                    (= last 0))
+            (error "FLAC block length %s is invalid" last))))
+  "FLAC metadata block header specification.")
+
+(defconst emms-info-native--flac-comment-block-bindat-spec
+  '((vendor-length u32r)
+    (eval (when (> last emms-info-native--max-vorbis-vendor-length)
+            (error "FLAC vendor length %s is too long" last)))
+    (vendor-string vec (vendor-length))
+    (user-comments-list-length u32r)
+    (eval (when (> last emms-info-native--max-num-vorbis-comments)
+            (error "FLAC user comment list length %s is too long"
+                   last)))
+    (user-comments repeat
+                   (user-comments-list-length)
+                   (struct emms-info-native--vorbis-comment-field-bindat-spec)))
+  "FLAC Vorbis comment block specification.")
+
+(defun emms-info-native--decode-flac-comments (filename)
+  "Read and decode comments from FLAC file FILENAME.
+Return comments in a list of (FIELD . VALUE) cons cells.  Only
+FIELDs that are listed in
+`emms-info-native--accepted-vorbis-fields' are returned."
+  (unless (emms-info-native--has-flac-signature filename)
+    (error "Invalid FLAC stream"))
+  (let* ((block (emms-info-native--decode-flac-comment-block
+                 filename))
+         (unpacked (bindat-unpack emms-info-native--flac-comment-block-bindat-spec
+                                  block))
+         (user-comments (bindat-get-field unpacked 'user-comments)))
+    (emms-info-native--extract-vorbis-comments user-comments)))
+
+(defun emms-info-native--has-flac-signature (filename)
+  "Check for FLAC stream marker at the beginning of FILENAME.
+Return t if there is a valid stream marker, nil otherwise."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (insert-file-contents-literally filename nil 0 4)
+    (looking-at "fLaC")))
+
+(defun emms-info-native--decode-flac-comment-block (filename)
+  "Read and decode a comment block from FLAC file FILENAME.
+Return the comment block data in a vector."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (let (comment-block
+          last-flag
+          (offset 4))
+      (while (and (not comment-block) (not last-flag))
+        (insert-file-contents-literally filename
+                                        nil
+                                        offset
+                                        (cl-incf offset 4))
+        (let* ((header (bindat-unpack emms-info-native--flac-metadata-block-header-bindat-spec
+                                      (buffer-string)))
+               (end (+ offset (bindat-get-field header 'length)))
+               (flags (bindat-get-field header 'flags))
+               (block-type (logand flags #x7F)))
+          (setq last-flag (> (logand flags #x80) 0))
+          (when (> block-type 6)
+            (error "FLAC block type error: expected <= 6, got %s"
+                   block-type))
+          (when (= block-type 4)
+            ;; Comment block found, extract it.
+            (insert-file-contents-literally filename nil offset end t)
+            (setq comment-block (vconcat (buffer-string))))
+          (setq offset end)))
+      comment-block)))
+
+;;;; id3v2 (MP3) code
+
+(defconst emms-info-native--id3v2-header-bindat-spec
+  '((file-identifier vec 3)
+    (eval (unless (equal last emms-info-native--id3v2-magic-array)
+            (error "id3v2 framing mismatch: expected `%s', got `%s'"
+                   emms-info-native--id3v2-magic-array
+                   last)))
+    (version u8)
+    (eval (setq emms-info-native--id3v2-version last))
+    (revision u8)
+    (flags bits 1)
+    (size-bytes vec 4)
+    (size eval (emms-info-native--checked-id3v2-size 'tag last)))
+  "id3v2 header specification.")
+
+(defconst emms-info-native--id3v2-magic-array
+  [#x49 #x44 #x33]
+  "id3v2 header magic pattern `ID3'.")
+
+(defconst emms-info-native--id3v2-frame-header-bindat-spec
+  '((id str (eval (if (= emms-info-native--id3v2-version 2) 3 4)))
+    (eval (unless (emms-info-native--valid-id3v2-frame-id-p last)
+            (error "id3v2 frame id `%s' is invalid" last)))
+    (size-bytes vec (eval (if (= emms-info-native--id3v2-version 2) 3 4)))
+    (size eval (emms-info-native--checked-id3v2-size 'frame last))
+    (flags bits (eval (if (= emms-info-native--id3v2-version 2) 0 2))))
+  "id3v2 frame header specification.")
+
+(defconst emms-info-native--id3v2-frame-to-info
+  '(("TAL"  . "album")
+    ("TALB" . "album")
+    ("TPE2" . "albumartist")
+    ("TSO2" . "albumartistsort")
+    ("TSOA" . "albumsort")
+    ("TP1"  . "artist")
+    ("TPE1" . "artist")
+    ("TSOP" . "artistsort")
+    ("TCM"  . "composer")
+    ("TCOM" . "composer")
+    ("TSOC" . "composersort")
+    ("TDRC" . "date")
+    ("TPA"  . "discnumber")
+    ("TPOS" . "discnumber")
+    ("TCON" . genre)
+    ("TPUB" . "label")
+    ("TDOR" . "originaldate")
+    ("TOR"  . "originalyear")
+    ("TORY" . "originalyear")
+    ("TIT2" . "title")
+    ("TT2"  . "title")
+    ("TSOT" . "titlesort")
+    ("TRK"  . "tracknumber")
+    ("TRCK" . "tracknumber")
+    ("TYE"  . "year")
+    ("TYER" . "year")
+    ("TXXX" . user-defined))
+  "Mapping from id3v2 frame identifiers to EMMS info fields.
+
+Sources:
+
+- URL `https://picard-docs.musicbrainz.org/en/appendices/tag_mapping.html'
+- URL `http://wiki.hydrogenaud.io/index.php?title=Foobar2000:ID3_Tag_Mapping'")
+
+(defconst emms-info-native--id3v1-genres
+  '((0 . "Blues")
+    (1 . "Classic Rock")
+    (2 . "Country")
+    (3 . "Dance")
+    (4 . "Disco")
+    (5 . "Funk")
+    (6 . "Grunge")
+    (7 . "Hip-Hop")
+    (8 . "Jazz")
+    (9 . "Metal")
+    (10 . "New Age")
+    (11 . "Oldies")
+    (12 . "Other")
+    (13 . "Pop")
+    (14 . "R&B")
+    (15 . "Rap")
+    (16 . "Reggae")
+    (17 . "Rock")
+    (18 . "Techno")
+    (19 . "Industrial")
+    (20 . "Alternative")
+    (21 . "Ska")
+    (22 . "Death Metal")
+    (23 . "Pranks")
+    (24 . "Soundtrack")
+    (25 . "Euro-Techno")
+    (26 . "Ambient")
+    (27 . "Trip-Hop")
+    (28 . "Vocal")
+    (29 . "Jazz+Funk")
+    (30 . "Fusion")
+    (31 . "Trance")
+    (32 . "Classical")
+    (33 . "Instrumental")
+    (34 . "Acid")
+    (35 . "House")
+    (36 . "Game")
+    (37 . "Sound Clip")
+    (38 . "Gospel")
+    (39 . "Noise")
+    (40 . "AlternRock")
+    (41 . "Bass")
+    (42 . "Soul")
+    (43 . "Punk")
+    (44 . "Space")
+    (45 . "Meditative")
+    (46 . "Instrumental Pop")
+    (47 . "Instrumental Rock")
+    (48 . "Ethnic")
+    (49 . "Gothic")
+    (50 . "Darkwave")
+    (51 . "Techno-Industrial")
+    (52 . "Electronic")
+    (53 . "Pop-Folk")
+    (54 . "Eurodance")
+    (55 . "Dream")
+    (56 . "Southern Rock")
+    (57 . "Comedy")
+    (58 . "Cult")
+    (59 . "Gangsta")
+    (60 . "Top 40")
+    (61 . "Christian Rap")
+    (62 . "Pop/Funk")
+    (63 . "Jungle")
+    (64 . "Native American")
+    (65 . "Cabaret")
+    (66 . "New Wave")
+    (67 . "Psychadelic")
+    (68 . "Rave")
+    (69 . "Showtunes")
+    (70 . "Trailer")
+    (71 . "Lo-Fi")
+    (72 . "Tribal")
+    (73 . "Acid Punk")
+    (74 . "Acid Jazz")
+    (75 . "Polka")
+    (76 . "Retro")
+    (77 . "Musical")
+    (78 . "Rock & Roll")
+    (79 . "Hard Rock")
+    (80 . "Folk")
+    (81 . "Folk-Rock")
+    (82 . "National Folk")
+    (83 . "Swing")
+    (84 . "Fast Fusion")
+    (85 . "Bebob")
+    (86 . "Latin")
+    (87 . "Revival")
+    (88 . "Celtic")
+    (89 . "Bluegrass")
+    (90 . "Avantgarde")
+    (91 . "Gothic Rock")
+    (92 . "Progressive Rock")
+    (93 . "Psychedelic Rock")
+    (94 . "Symphonic Rock")
+    (95 . "Slow Rock")
+    (96 . "Big Band")
+    (97 . "Chorus")
+    (98 . "Easy Listening")
+    (99 . "Acoustic")
+    (100 . "Humour")
+    (101 . "Speech")
+    (102 . "Chanson")
+    (103 . "Opera")
+    (104 . "Chamber Music")
+    (105 . "Sonata")
+    (106 . "Symphony")
+    (107 . "Booty Bass")
+    (108 . "Primus")
+    (109 . "Porn Groove")
+    (110 . "Satire")
+    (111 . "Slow Jam")
+    (112 . "Club")
+    (113 . "Tango")
+    (114 . "Samba")
+    (115 . "Folklore")
+    (116 . "Ballad")
+    (117 . "Power Ballad")
+    (118 . "Rhythmic Soul")
+    (119 . "Freestyle")
+    (120 . "Duet")
+    (121 . "Punk Rock")
+    (122 . "Drum Solo")
+    (123 . "A cappella")
+    (124 . "Euro-House")
+    (125 . "Dance Hall"))
+  "id3v1 genres.")
+
+(defconst emms-info-native--id3v2-text-encodings
+  '((0 . latin-1)
+    (1 . utf-16)
+    (2 . uft-16be)
+    (3 . utf-8))
+  "id3v2 text encodings.")
+
+(defun emms-info-native--valid-id3v2-frame-id-p (id)
+  "Return t if ID is a proper id3v2 frame identifier, nil otherwise."
+  (if (= emms-info-native--id3v2-version 2)
+      (string-match "[A-Z0-9]\\{3\\}" id)
+    (string-match "[A-Z0-9]\\{4\\}" id)))
+
+(defun emms-info-native--checked-id3v2-size (elt bytes)
+  "Calculate id3v2 element ELT size from BYTES.
+ELT must be either \\='tag or \\='frame.
+
+Return the size.  Signal an error if the size is zero."
+  (let ((size (cond ((eq elt 'tag)
+                     (emms-info-native--decode-id3v2-size bytes t))
+                    ((eq elt 'frame)
+                     (if (= emms-info-native--id3v2-version 4)
+                         (emms-info-native--decode-id3v2-size bytes t)
+                       (emms-info-native--decode-id3v2-size bytes nil))))))
+    (if (zerop size)
+        (error "id3v2 tag/frame size is zero")
+      size)))
+
+(defun emms-info-native--decode-id3v2-size (bytes syncsafe)
+  "Decode id3v2 element size from BYTES.
+Depending on SYNCSAFE, BYTES are interpreted as 7- or 8-bit
+bytes, MSB first.
+
+Return the decoded size."
+  (let ((num-bits (if syncsafe 7 8)))
+    (apply '+ (seq-map-indexed (lambda (elt idx)
+                                 (* (expt 2 (* num-bits idx)) elt))
+                               (reverse bytes)))))
+
+(defun emms-info-native--decode-id3v2 (filename)
+  "Read and decode id3v2 metadata from FILENAME.
+Return metadata in a list of (FIELD . VALUE) cons cells, or nil
+in case of errors or if there were no known fields in FILENAME.
+
+See `emms-info-native--id3v2-frame-to-info' for recognized
+fields."
+  (condition-case nil
+      (let* (emms-info-native--id3v2-version
+             (header (emms-info-native--decode-id3v2-header filename))
+             (tag-size (bindat-get-field header 'size))
+             (unsync (memq 7 (bindat-get-field header 'flags)))
+             (offset 10))
+        (when (memq 6 (bindat-get-field header 'flags))
+          ;; Skip the extended header.
+          (cl-incf offset
+                   (emms-info-native--checked-id3v2-ext-header-size filename)))
+        (emms-info-native--decode-id3v2-frames filename
+                                               offset
+                                               (+ tag-size 10)
+                                               unsync))
+    (error nil)))
+
+(defun emms-info-native--decode-id3v2-header (filename)
+  "Read and decode id3v2 header from FILENAME."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (insert-file-contents-literally filename nil 0 10)
+    (bindat-unpack emms-info-native--id3v2-header-bindat-spec
+                   (buffer-string))))
+
+(defun emms-info-native--checked-id3v2-ext-header-size (filename)
+  "Read and decode id3v2 extended header size from FILENAME.
+Return the size.  Signal an error if the size is zero."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (insert-file-contents-literally filename nil 10 14)
+    (emms-info-native--checked-id3v2-size 'frame (buffer-string))))
+
+(defun emms-info-native--decode-id3v2-frames (filename begin end unsync)
+  "Read and decode id3v2 text frames from FILENAME.
+BEGIN should be the offset of first byte of the first frame, and
+END should be the offset after the complete id3v2 tag.
+
+If UNSYNC is t, the frames are assumed to have gone through
+unsynchronization and decoded as such.
+
+Return metadata in a list of (FIELD . VALUE) cons cells."
+  (let ((offset begin)
+        (limit (- end (emms-info-native--id3v2-frame-header-size)))
+        comments)
+    (condition-case nil
+        (while (< offset limit)
+          (let* ((frame-data (emms-info-native--decode-id3v2-frame filename
+                                                                   offset
+                                                                   unsync))
+                 (next-frame-offset (car frame-data))
+                 (comment (cdr frame-data)))
+            (when comment (push comment comments))
+            (setq offset next-frame-offset)))
+      (error nil))
+    comments))
+
+(defun emms-info-native--id3v2-frame-header-size ()
+  "Return the last decoded header size in bytes."
+  (if (= emms-info-native--id3v2-version 2) 6 10))
+
+(defun emms-info-native--decode-id3v2-frame (filename offset unsync)
+  (let* ((header (emms-info-native--decode-id3v2-frame-header filename
+                                                              offset))
+         (info-id (emms-info-native--id3v2-frame-info-id header))
+         (data-offset (car header))
+         (size (bindat-get-field (cdr header) 'size)))
+    (if (or info-id unsync)
+        ;; Note that if unsync is t, we have to always read the frame
+        ;; to determine next-frame-offset.
+        (let* ((data (emms-info-native--read-id3v2-frame-data filename
+                                                              data-offset
+                                                              size
+                                                              unsync))
+               (next-frame-offset (car data))
+               (value (emms-info-native--decode-id3v2-frame-data (cdr data)
+                                                                 info-id)))
+          (cons next-frame-offset value))
+      ;; Skip the frame.
+      (cons (+ data-offset size) nil))))
+
+(defun emms-info-native--decode-id3v2-frame-header (filename begin)
+  "Read and decode id3v2 frame header from FILENAME.
+Start reading from offset BEGIN.
+
+Return a cons cell (OFFSET . FRAME), where OFFSET is the byte
+offset after the frame header, and FRAME is the decoded frame."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (let ((end (+ begin (emms-info-native--id3v2-frame-header-size))))
+      (insert-file-contents-literally filename nil begin end)
+      (cons end (bindat-unpack emms-info-native--id3v2-frame-header-bindat-spec
+                               (buffer-string))))))
+
+(defun emms-info-native--id3v2-frame-info-id (frame)
+  "Return the emms-info identifier for FRAME.
+If there is no such identifier, return nil."
+  (cdr (assoc (bindat-get-field frame 'id)
+              emms-info-native--id3v2-frame-to-info)))
+
+(defun emms-info-native--read-id3v2-frame-data (filename
+                                                begin
+                                                num-bytes
+                                                unsync)
+  "Read NUM-BYTES of raw id3v2 frame data from FILENAME.
+Start reading from offset BEGIN.  If UNSYNC is t, all 'FF 00'
+byte combinations are replaced by 'FF'.  Replaced byte pairs are
+counted as one, instead of two, towards NUM-BYTES.
+
+Return a cons cell (OFFSET . DATA), where OFFSET is the byte
+offset after NUM-BYTES bytes have been read, and DATA is the raw
+data."
+  (with-temp-buffer
+    (set-buffer-multibyte nil)
+    (if unsync
+        ;; Reverse unsynchronization.
+        (let ((peek-end (+ begin (* 2 num-bytes)))
+              (end num-bytes))
+          (insert-file-contents-literally filename nil begin peek-end)
+          (goto-char (point-min))
+          (while (and (re-search-forward (string 255 0) nil t)
+                      (< (point) end))
+            (replace-match (string 255))
+            (cl-incf end 1))
+          (delete-region (1+ num-bytes) (point-max))
+          (cons (+ begin end) (buffer-string)))
+      ;; No unsynchronization: read the data as-is.
+      (let ((end (+ begin num-bytes)))
+        (insert-file-contents-literally filename nil begin end)
+        (cons end (buffer-string))))))
+
+(defun emms-info-native--decode-id3v2-frame-data (data info-id)
+  "Decode id3v2 text frame data DATA.
+If INFO-ID is `user-defined', assume that DATA is a TXXX frame
+with key/value-pair.  Extract the key and, if it is a mapped
+element in `emms-info-native--id3v2-frame-to-info', use it as
+INFO-ID.
+
+If INFO-ID is `genre', assume that DATA is either an integral
+id3v1 genre reference or a plain genre string.  In the former
+case map the reference to a string via
+`emms-info-native--id3v1-genres'; in the latter case use the
+genre string verbatim.
+
+Return a cons cell (INFO-ID . VALUE) where VALUE is the decoded
+string."
+  (when info-id
+    (let ((str (emms-info-native--decode-id3v2-string data)))
+      (cond ((stringp info-id) (cons info-id str))
+            ((eq info-id 'genre)
+             (if (string-match "^(?\\([0-9]+\\))?" str)
+                 (let ((v1-genre (assoc (string-to-number (match-string 1 str))
+                                        emms-info-native--id3v1-genres)))
+                   (when v1-genre (cons "genre" (cdr v1-genre))))
+               (cons "genre" str)))
+            ((eq info-id 'user-defined)
+             (let* ((key-val (split-string str (string 0)))
+                    (key (downcase (car key-val)))
+                    (val (cadr key-val)))
+               (when (rassoc key emms-info-native--id3v2-frame-to-info)
+                 (cons key val))))))))
+
+(defun emms-info-native--decode-id3v2-string (bytes)
+  "Decode id3v2 text information from BYTES.
+Remove the terminating null byte, if any.
+
+Return the text as string."
+  (let* ((encoding (emms-info-native--id3v2-text-encoding bytes))
+         (string (mapconcat #'byte-to-string (seq-rest bytes) ""))
+         (decoded (decode-coding-string string encoding)))
+    (when (> (length decoded) 0)
+      (if (equal (substring decoded -1) "\0")
+          (substring decoded 0 -1)
+        decoded))))
+
+(defun emms-info-native--id3v2-text-encoding (bytes)
+  "Return the encoding for text information BYTES."
+  (cdr (assoc (seq-first bytes)
+              emms-info-native--id3v2-text-encodings)))
+
+;;;; EMMS code
+
+(defun emms-info-native (track)
+  "Set info fields for TRACK.
+Supports Ogg Vorbis/Opus, FLAC, and MP3 files."
+  (condition-case env
+      (let* ((filename (emms-track-name track))
+             (info-fields (emms-info-native--decode-info-fields filename)))
+	(dolist (field info-fields)
+	  (let ((name (intern (concat "info-" (car field))))
+		(value (cdr field)))
+            (unless (zerop (length value))
+              (emms-track-set track
+                              name
+                              (if (eq name 'info-playing-time)
+				  (string-to-number value)
+				(string-trim-right value)))))))
+    (error (message "emms-info-native error processing %s: %s"
+		    (emms-track-name track) env))))
+
+(defun emms-info-native--decode-info-fields (filename)
+  "Decode info fields from FILENAME.
+Return a list of (FIELD . VALUE) cons cells, where FIELD is an
+info field and VALUE is the corresponding info value.  Both are
+strings."
+  (let ((stream-type (emms-info-native--find-stream-type filename)))
+    (cond ((or (eq stream-type 'vorbis) (eq stream-type 'opus))
+           (emms-info-native--decode-ogg-comments filename stream-type))
+          ((eq stream-type 'flac)
+           (emms-info-native--decode-flac-comments filename))
+          ((eq stream-type 'mp3)
+           (emms-info-native--decode-id3v2 filename))
+	  ((eq stream-type 'spc)
+	   (emms-info-spc--decode-id666 filename))
+          (t nil))))
+
+(defun emms-info-native--find-stream-type (filename)
+  "Deduce the stream type from FILENAME.
+This is a naive implementation that relies solely on filename
+extension.
+
+Return one of symbols `vorbis', `opus', `flac', or `mp3'."
+  (let ((case-fold-search t))
+    (cond ((string-match ".ogg$" filename) 'vorbis)
+          ((string-match ".opus$" filename) 'opus)
+          ((string-match ".flac$" filename) 'flac)
+          ((string-match ".mp3$" filename) 'mp3)
+	  ((string-match ".spc$" filename) 'spc)
+          (t nil))))
+
+(provide 'emms-info-native)
+
+;;; emms-info-native.el ends here