feat(music): Switch EMMS from MPD to MPV backend

Major improvements to music player configuration:

Backend Changes:
- Switch from emms-player-mpd to emms-player-mpv
- Remove MPD daemon dependency (no service management required)
- Configure MPV with --quiet, --no-video, --audio-display flags
- Support both local files and streaming URLs (http/https/mms)

Keybinding Enhancements:
- Add C-; m n → next track
- Add C-; m p → previous track
- Add C-; m g → go to playlist
- In playlist: n/P for next/prev, f/b for seek forward/backward
- Update which-key descriptions

Code Quality:
- Use music-dir constant from user-constants.el (not hardcoded path)
- Add (require 'user-constants) for proper dependency
- Update commentary to reflect MPV backend

Test Fixes:
- Fix 8 failing append-track tests
- Update test mock data to use cj/music-root for portability
- All 104 music-config tests now passing

Benefits:
- No daemon to start/stop/manage
- Simpler architecture (one process vs MPD+EMMS)
- Streaming radio URLs work out of the box
- Better path consistency across codebase

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

2 files changed, 63 insertions, 51 deletions

diff --git a/modules/music-config.el b/modules/music-config.el
index cdbe56e0..0994bf82 100644
--- a/modules/music-config.el
+++ b/modules/music-config.el
@@ -1,8 +1,8 @@
-;;; music-config.el --- EMMS configuration with MPD integration -*- coding: utf-8; lexical-binding: t; -*-
+;;; music-config.el --- EMMS configuration with MPV backend -*- coding: utf-8; lexical-binding: t; -*-
 ;;
 ;;; Commentary:
 ;;
-;; Comprehensive music management in Emacs via EMMS with MPD backend.
+;; Comprehensive music management in Emacs via EMMS with MPV backend.
 ;; Focus: simple, modular helpers; consistent error handling; streamlined UX.
 ;;
 ;; Highlights:
@@ -10,17 +10,18 @@
 ;; - Recursive directory add
 ;; - Dired/Dirvish integration (add selection)
 ;; - M3U playlist save/load/edit/reload
-;; - Radio station M3U creation
+;; - Radio station M3U creation (streaming URLs supported)
 ;; - Playlist window toggling
-;; - MPD as player
+;; - MPV as player (no daemon required)
 ;;
 ;;; Code:
 
 (require 'subr-x)
+(require 'user-constants)
 
 ;;; Settings (no Customize)
 
-(defvar cj/music-root (expand-file-name "~/music")
+(defvar cj/music-root music-dir
   "Root directory of your music collection.")
 
 (defvar cj/music-m3u-root cj/music-root
@@ -421,7 +422,9 @@ Dirs added recursively."
   "r" #'cj/music-create-radio-station
   "SPC" #'emms-pause
   "s" #'emms-stop
-  "p" #'emms-playlist-mode-go
+  "n" #'emms-next
+  "p" #'emms-previous
+  "g" #'emms-playlist-mode-go
   "x" #'emms-shuffle)
 
 (keymap-set cj/custom-keymap "m" cj/music-map)
@@ -434,7 +437,9 @@ Dirs added recursively."
     "C-; m r" "create radio"
     "C-; m SPC" "pause"
     "C-; m s" "stop"
-    "C-; m p" "playlist mode"
+    "C-; m n" "next track"
+    "C-; m p" "previous track"
+    "C-; m g" "goto playlist"
     "C-; m x" "shuffle"))
 
 (use-package emms
@@ -445,7 +450,7 @@ Dirs added recursively."
   :commands (emms-mode-line-mode)
   :config
   (require 'emms-setup)
-  (require 'emms-player-mpd)
+  (require 'emms-player-mpv)
   (require 'emms-playlist-mode)
   (require 'emms-source-file)
   (require 'emms-source-playlist)
@@ -454,8 +459,8 @@ Dirs added recursively."
   (setq emms-source-file-default-directory cj/music-root)
   (setq emms-playlist-default-major-mode 'emms-playlist-mode)
 
-  ;; Use only MPD as player - MUST be set before emms-all
-  (setq emms-player-list '(emms-player-mpd))
+  ;; Use MPV as player - MUST be set before emms-all
+  (setq emms-player-list '(emms-player-mpv))
 
   ;; Now initialize EMMS
   (emms-all)
@@ -464,22 +469,18 @@ Dirs added recursively."
   (emms-playing-time-disable-display)
   (emms-mode-line-mode -1)
 
-  ;; MPD configuration
-  (setq emms-player-mpd-server-name "localhost")
-  (setq emms-player-mpd-server-port "6600")
-  (setq emms-player-mpd-music-directory cj/music-root)
-  (condition-case err
-      (emms-player-mpd-connect)
-    (error (message "Failed to connect to MPD: %s" err)))
-
-  ;; note setopt as variable is customizeable
-  ;; MPD can play both local files and stream URLs
-  (setopt emms-player-mpd-supported-regexp
-          (rx (or
-               ;; Stream URLs
-               (seq bos (or "http" "https" "mms") "://")
-               ;; Local music files by extension
-               (regexp (apply #'emms-player-simple-regexp cj/music-file-extensions)))))
+  ;; MPV configuration
+  ;; MPV supports both local files and stream URLs
+  (setq emms-player-mpv-parameters
+        '("--quiet" "--no-video" "--audio-display=no"))
+
+  ;; Update supported file types for mpv player
+  (setq emms-player-mpv-regexp
+        (rx (or
+             ;; Stream URLs
+             (seq bos (or "http" "https" "mms") "://")
+             ;; Local music files by extension
+             (seq "." (or "aac" "flac" "m4a" "mp3" "ogg" "opus" "wav") eos))))
 
   ;; Keep cj/music-playlist-file in sync if playlist is cleared
   (defun cj/music--after-playlist-clear (&rest _)
@@ -497,6 +498,10 @@ Dirs added recursively."
         ("p"   . emms-playlist-mode-go)
         ("SPC" . emms-pause)
         ("s"   . emms-stop)
+        ("n"   . emms-next)
+        ("P"   . emms-previous)
+        ("f"   . emms-seek-forward)
+        ("b"   . emms-seek-backward)
         ("x"   . emms-shuffle)
         ("q"   . emms-playlist-mode-bury-buffer)
         ("a"   . cj/music-fuzzy-select-and-add)
@@ -512,7 +517,7 @@ Dirs added recursively."
         ("C-<down>" . emms-playlist-mode-shift-track-down)
         ;; Radio
         ("r" . cj/music-create-radio-station)
-        ;; Volume (MPD)
+        ;; Volume (MPV)
         ("-" . emms-volume-lower)
         ("=" . emms-volume-raise)))
 
diff --git a/tests/test-music-config--append-track-to-m3u-file.el b/tests/test-music-config--append-track-to-m3u-file.el
index 2bf3e87d..be0cbd8e 100644
--- a/tests/test-music-config--append-track-to-m3u-file.el
+++ b/tests/test-music-config--append-track-to-m3u-file.el
@@ -40,39 +40,42 @@
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
       (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
-             (track-path "/home/user/music/artist/song.mp3"))
+             (track-path (expand-file-name "artist/song.mp3" cj/music-root))
+             (expected-relative "artist/song.mp3"))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
-          (should (string= (buffer-string) (concat track-path "\n")))))
+          (should (string= (buffer-string) (concat expected-relative "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-normal-existing-with-newline-appends-track ()
   "Append to file with existing content ending with newline."
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
-      (let* ((existing-content "/home/user/music/first.mp3\n")
+      (let* ((existing-content "first.mp3\n")
              (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
-             (track-path "/home/user/music/second.mp3"))
+             (track-path (expand-file-name "second.mp3" cj/music-root))
+             (expected-relative "second.mp3"))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
           (should (string= (buffer-string)
-                          (concat existing-content track-path "\n")))))
+                          (concat existing-content expected-relative "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-normal-existing-without-newline-appends-track ()
   "Append to file without trailing newline adds leading newline."
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
-      (let* ((existing-content "/home/user/music/first.mp3")
+      (let* ((existing-content "first.mp3")
              (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
-             (track-path "/home/user/music/second.mp3"))
+             (track-path (expand-file-name "second.mp3" cj/music-root))
+             (expected-relative "second.mp3"))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
           (should (string= (buffer-string)
-                          (concat existing-content "\n" track-path "\n")))))
+                          (concat existing-content "\n" expected-relative "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-normal-multiple-appends-all-succeed ()
@@ -80,9 +83,11 @@
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
       (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
-             (track1 "/home/user/music/track1.mp3")
-             (track2 "/home/user/music/track2.mp3")
-             (track1-duplicate "/home/user/music/track1.mp3"))
+             (track1 (expand-file-name "track1.mp3" cj/music-root))
+             (track2 (expand-file-name "track2.mp3" cj/music-root))
+             (track1-duplicate (expand-file-name "track1.mp3" cj/music-root))
+             (rel1 "track1.mp3")
+             (rel2 "track2.mp3"))
         (cj/music--append-track-to-m3u-file track1 m3u-file)
         (cj/music--append-track-to-m3u-file track2 m3u-file)
         (cj/music--append-track-to-m3u-file track1-duplicate m3u-file)
@@ -90,7 +95,7 @@
           (insert-file-contents m3u-file)
           (let ((content (buffer-string)))
             (should (string= content
-                            (concat track1 "\n" track2 "\n" track1-duplicate "\n"))))))
+                            (concat rel1 "\n" rel2 "\n" rel1 "\n"))))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 ;;; Boundary Cases
@@ -100,15 +105,14 @@
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
       (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
-             ;; Create a path that's ~500 chars long
-             (track-path (concat "/home/user/music/"
-                                (make-string 450 ?a)
-                                "/song.mp3")))
+             ;; Create a relative path that's ~450 chars long
+             (relative-path (concat (make-string 440 ?a) "/song.mp3"))
+             (track-path (expand-file-name relative-path cj/music-root)))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
-          (should (string= (buffer-string) (concat track-path "\n")))
-          (should (= (length (buffer-string)) (1+ (length track-path))))))
+          (should (string= (buffer-string) (concat relative-path "\n")))
+          (should (= (length (buffer-string)) (1+ (length relative-path))))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-boundary-path-with-unicode-appends-successfully ()
@@ -116,11 +120,12 @@
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
       (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
-             (track-path "/home/user/music/中文/artist-名前/song🎵.mp3"))
+             (relative-path "中文/artist-名前/song🎵.mp3")
+             (track-path (expand-file-name relative-path cj/music-root)))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
-          (should (string= (buffer-string) (concat track-path "\n")))))
+          (should (string= (buffer-string) (concat relative-path "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-boundary-path-with-spaces-appends-successfully ()
@@ -128,11 +133,12 @@
   (test-music-config--append-track-to-m3u-file-setup)
   (unwind-protect
       (let* ((m3u-file (cj/create-temp-test-file "test-playlist-"))
-             (track-path "/home/user/music/Artist Name/Album (2024)/01 - Song's Title [Remix].mp3"))
+             (relative-path "Artist Name/Album (2024)/01 - Song's Title [Remix].mp3")
+             (track-path (expand-file-name relative-path cj/music-root)))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
-          (should (string= (buffer-string) (concat track-path "\n")))))
+          (should (string= (buffer-string) (concat relative-path "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 (ert-deftest test-music-config--append-track-to-m3u-file-boundary-m3u-with-comments-appends-after ()
@@ -141,12 +147,13 @@
   (unwind-protect
       (let* ((existing-content "#EXTM3U\n#EXTINF:-1,Radio Station\nhttp://stream.url/radio\n")
              (m3u-file (cj/create-temp-test-file-with-content existing-content "test-playlist-"))
-             (track-path "/home/user/music/local-track.mp3"))
+             (relative-path "local-track.mp3")
+             (track-path (expand-file-name relative-path cj/music-root)))
         (cj/music--append-track-to-m3u-file track-path m3u-file)
         (with-temp-buffer
           (insert-file-contents m3u-file)
           (should (string= (buffer-string)
-                          (concat existing-content track-path "\n")))))
+                          (concat existing-content relative-path "\n")))))
     (test-music-config--append-track-to-m3u-file-teardown)))
 
 ;;; Error Cases