Monday, March 18, 2024

Smart Media Selector For The Emacspeak Audio Desktop

Smart Media Selector For The Audio Desktop

1. Overview

I have over 60MB of audio content on my laptop spread across 755 subdirecories in over 9100 files. I also have many Internet stream shortcuts that I listen to on a regular basis.

This blog article outlines the media selector implementation in Emacspeak and shows how a small amount of Lisp code built atop Emacs' built-in affordances of completion provides a light-weight yet efficient interface. Notice that the implementation does not involve fancy things like SQL databases, MP3 tags that one needs to update etc.; the solution relies on the speed of today's laptops, especially given the speed of disk access.

2. User Experience

As I type this up, the set of requirements as expressed in English is far more verbose (and likely more complicated) than its expression in Lisp!

2.1. Pre-requisites for content selection and playback

  1. Launch either MPV (via package empv.el) or mplayer via Emacspeak's emacspeak-mplayer with a few keystrokes.
  2. Media selection uses ido with fuzzy matching.
  3. Choices are filtered incrementally for efficient eyes-free interaction; see the relevant blog article on Search, Input, Filter, Target for additional background.
  4. Content can be filtered using the directory structure, where directories conceptually equate to music albums, audio books or othre logical content groups.Once selected, a directory and its contents are played as a conceptual play-list.
  5. Searching and filtering can also occur across the list of all 9,100+ media files spread across 700+ directories.
  6. Starting point of the SIFT process should be influenced by one's current context, e.g., default-directory.
  7. Each step of this process should have reasonable fallbacks.

3. Mapping Design To Implementation

  1. Directory where we start AKA context is selected by function emacspeak-media-guess-directory.
    1. If default directory matches emacspeak-media-directory-regexp,use it.
    2. If default directory contains media files, then use it.
    3. If default directory contains directory emacspeak-media — then use it.
    4. Otherwise use emacspeak-media-shortcuts as the fallback.
  2. Once we have selected the context, function emacspeak-media-read-resourceuses ido style interaction with fuzzy-matching to pick the file to play.
  3. That function uses Emacs' built-in directory-files-recursively to build the collection to hand-off to completing-read; It uses an Emacspeak provided function ems–subdirs-recursively to build up the list of 755+ sub-directories that live under $XDGMUSICDIR.

4. Resulting Experience

  1. I can pick the media to play with a few keystrokes.
  2. I use Emacs' repeat-mode to advantage whereby I can quickly change volume etc once content is playing before going back to work.
  3. There's no media-player UI to get in my way while working, but I can stop playing media with a single keystroke.
  4. Most importantly, I dont have to tag media, maintain databases or do other busy work to be able to launch the media that I want!

5. The Lisp Code

The hyperlinks to the Emacspeak code-base are the source of truth. I'll include a snapshot of the functions mentioned above for completeness.

5.1. Guess Context

  (defun emacspeak-media-guess-directory ()
  "Guess media directory.
1. If default directory matches emacspeak-media-directory-regexp,use it.
2.  If default directory contains media files, then use it.
3. If default directory contains directory emacspeak-media --- then use it.
4. Otherwise use emacspeak-media-shortcuts as the fallback."
  (cl-declare (special emacspeak-media-directory-regexp
                       emacspeak-media emacspeak-m-player-hotkey-p))
  (let ((case-fold-search t))
    (cond
     ((or (eq major-mode 'dired-mode) (eq major-mode 'locate-mode)) nil)
     (emacspeak-m-player-hotkey-p   emacspeak-media-shortcuts)
     ((or                               ;  dir  contains media:
       (string-match emacspeak-media-directory-regexp default-directory)
       (directory-files default-directory   nil emacspeak-media-extensions))
      default-directory)
     ((file-in-directory-p emacspeak-media default-directory) emacspeak-media)
     (t   emacspeak-media-shortcuts))))

5.2. Read Resource

(defun emacspeak-media-read-resource (&optional prefix)
  "Read resource from minibuffer.
If a dynamic playlist exists, just use it."
  (cl-declare (special emacspeak-media-dynamic-playlist
                       emacspeak-m-player-hotkey-p))
  (cond
   (emacspeak-media-dynamic-playlist nil) ; do nothing if dynamic playlist
   (emacspeak-m-player-hotkey-p (emacspeak-media-local-resource prefix))
   (t                               ; not hotkey, not dynamic playlist
    (let* ((completion-ignore-case t)
           (read-file-name-completion-ignore-case t)
           (filename
            (when (memq major-mode '(dired-mode locate-mode))
              (dired-get-filename 'local 'no-error)))
           (dir (emacspeak-media-guess-directory))
           (collection
            (or
             filename                   ; short-circuit expensive call
             (if prefix
                 (ems--subdirs-recursively  dir) ;list dirs
               (directory-files-recursively dir emacspeak-media-extensions)))))
      (or filename (completing-read "Media: "  collection))))))

5.3. Helper: Recursive List Of Sub-directories

  ;;; Helpers: subdirs


(defconst ems--subdirs-filter
  (eval-when-compile
    (concat (regexp-opt '("/.." "/." "/.git")) "$"))
  "Pattern to filter out dirs during traversal.")

(defsubst ems--subdirs (d)
  "Return list of subdirs in directory d"
  (cl-remove-if-not #'file-directory-p (cddr (directory-files d 'full))))

(defun ems--subdirs-recursively (d)
  "Recursive list of  subdirs"
  (cl-declare (special ems--subdirs-filter))
  (let ((result (list d))
        (subdirs (ems--subdirs d)))
    (cond
     ((string-match ems--subdirs-filter d) nil)                              ; pass
     (t
      (cl-loop
       for dir in subdirs
       if (not (string-match ems--subdirs-filter dir)) do
       (setq result  (nconc result (ems--subdirs-recursively dir))))))
    result))
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