feat(transcription): extend dired T to transcribe videos via ffmpeg, with tests

Pressing `T' in dired/dirvish on an audio file already transcribed
it; on a video file it bounced with "Not an audio file".  Real
recordings ship as .mp4 / .mkv at least as often as raw .m4a, so
the one-key flow ended at the wrong place.

Pipeline now:
- audio path -> direct into `cj/--start-transcription-process'
  (unchanged).
- video path -> async ffmpeg extracts the audio track to a temp
  .mp3 under `temporary-file-directory' (libmp3lame, VBR q:a 4,
  ~165kbps -- right size for speech, accepted by every backend),
  then transcribes that file with the temp marked for cleanup
  after the transcription sentinel fires.

Surface changes:
- `cj/video-file-extensions' added to user-constants.el (mp4, mkv,
  mov, webm, avi, m4v, wmv, flv, mpg, mpeg, 3gp, ogv).
- New predicates `cj/--video-file-p' / `cj/--media-file-p'.
- New `cj/--extract-audio-from-video' (async ffmpeg with success
  callback; surfaces `cj/--notify' on failure; user-errors if
  ffmpeg isn't on PATH).
- `cj/--start-transcription-process' gains optional `cleanup-file'.
  Sentinel deletes it after the existing logic runs.  Backwards
  compatible -- the audio flow doesn't pass it.
- `cj/transcribe-audio' renamed to `cj/transcribe-media' (dispatcher
  on audio vs video).  `cj/transcribe-audio-at-point' renamed to
  `cj/transcribe-media-at-point'.  Both old names kept as
  `defalias' so M-x history and any external references still work.
- `T' in dired-mode-map + dirvish-mode-map points at
  `cj/transcribe-media-at-point'.
- Module commentary USAGE block updated.

15 new ERT tests in `tests/test-transcription-video.el' cover the
predicates (happy/boundary/error), ffmpeg invocation (correct args
+ missing-ffmpeg path), the dispatcher (audio direct, video via
extraction, non-media rejected), the aliases, and the T binding.
One existing test in `test-transcription-status-and-commands.el'
updated to stub the new delegate name.

Verified locally that ffmpeg is on PATH with libmp3lame, and that
the exact arg list my code uses produces a valid MP3 from a
synthetic test video.

2 files changed, 163 insertions, 2 deletions

diff --git a/tests/test-transcription-status-and-commands.el b/tests/test-transcription-status-and-commands.el
index 90841e70..7c796de0 100644
--- a/tests/test-transcription-status-and-commands.el
+++ b/tests/test-transcription-status-and-commands.el
@@ -179,13 +179,18 @@
     (should-error (cj/transcribe-audio-at-point) :type 'user-error)))
 
 (ert-deftest test-tx-transcribe-audio-at-point-normal-delegates ()
-  "Normal: with a file at point, delegates to `cj/transcribe-audio'."
+  "Normal: with a file at point, delegates to `cj/transcribe-media'.
+
+`cj/transcribe-audio-at-point' is now a `defalias' for
+`cj/transcribe-media-at-point', which hands off to
+`cj/transcribe-media' (no longer the old audio-only command).  The
+stub still pins behavior by name."
   (let ((handed-off nil))
     (cl-letf (((symbol-function 'derived-mode-p)
                (lambda (&rest modes) (memq 'dired-mode modes)))
               ((symbol-function 'dired-get-filename)
                (lambda (&rest _) "/tmp/recording.wav"))
-              ((symbol-function 'cj/transcribe-audio)
+              ((symbol-function 'cj/transcribe-media)
                (lambda (f) (setq handed-off f))))
       (cj/transcribe-audio-at-point))
     (should (equal handed-off "/tmp/recording.wav"))))
diff --git a/tests/test-transcription-video.el b/tests/test-transcription-video.el
new file mode 100644
index 00000000..8327fa32
--- /dev/null
+++ b/tests/test-transcription-video.el
@@ -0,0 +1,156 @@
+;;; test-transcription-video.el --- Tests for video transcription dispatch -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for the video branch of the transcription pipeline.  Audio
+;; files keep flowing through `cj/--start-transcription-process'
+;; unchanged (covered by sibling test files).  Video files go through
+;; ffmpeg audio extraction first, then into the same transcription
+;; pipeline with the extracted file marked for cleanup once
+;; transcription completes.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'transcription-config)
+
+;;; cj/--video-file-p
+
+(ert-deftest test-tx-video-file-p-recognizes-common-video-extensions ()
+  "Normal: common video extensions are recognized."
+  (dolist (path '("clip.mp4" "talk.mkv" "demo.mov" "ad.webm" "old.avi"
+                  "screencast.m4v" "promo.mpg"))
+    (should (cj/--video-file-p path))))
+
+(ert-deftest test-tx-video-file-p-rejects-audio-and-non-media-extensions ()
+  "Boundary: audio and unrelated extensions return nil."
+  (dolist (path '("song.mp3" "notes.txt" "image.png" "archive.tar.gz"))
+    (should-not (cj/--video-file-p path))))
+
+(ert-deftest test-tx-video-file-p-case-insensitive ()
+  "Boundary: uppercase extensions count too."
+  (should (cj/--video-file-p "Clip.MP4"))
+  (should (cj/--video-file-p "TALK.MKV")))
+
+(ert-deftest test-tx-video-file-p-handles-no-extension ()
+  "Boundary: extensionless and nil/empty input returns nil."
+  (should-not (cj/--video-file-p "README"))
+  (should-not (cj/--video-file-p ""))
+  (should-not (cj/--video-file-p nil)))
+
+;;; cj/--media-file-p
+
+(ert-deftest test-tx-media-file-p-accepts-audio ()
+  "Normal: audio passes."
+  (should (cj/--media-file-p "song.mp3")))
+
+(ert-deftest test-tx-media-file-p-accepts-video ()
+  "Normal: video passes."
+  (should (cj/--media-file-p "clip.mp4")))
+
+(ert-deftest test-tx-media-file-p-rejects-non-media ()
+  "Boundary: text, image, etc. fail."
+  (should-not (cj/--media-file-p "notes.txt"))
+  (should-not (cj/--media-file-p "image.png")))
+
+;;; cj/--extract-audio-from-video
+
+(ert-deftest test-tx-extract-audio-invokes-ffmpeg-with-expected-args ()
+  "Normal: extraction shells ffmpeg with -vn and the chosen MP3 encoder."
+  (let* ((video "/clips/demo.mp4")
+         (out "/tmp/cj-tx-extract.mp3")
+         make-process-kwargs)
+    (cl-letf (((symbol-function 'cj/executable-find-or-warn)
+               (lambda (&rest _) "/usr/bin/ffmpeg"))
+              ((symbol-function 'make-process)
+               (lambda (&rest kw) (setq make-process-kwargs kw) 'fake-process)))
+      (cj/--extract-audio-from-video video out #'ignore))
+    (should make-process-kwargs)
+    (let ((cmd (plist-get make-process-kwargs :command)))
+      (should (equal (car cmd) "/usr/bin/ffmpeg"))
+      (should (member "-vn" cmd))
+      (should (member video cmd))
+      (should (member out cmd))
+      (should (member "libmp3lame" cmd)))))
+
+(ert-deftest test-tx-extract-audio-errors-when-ffmpeg-missing ()
+  "Error: ffmpeg not on PATH signals user-error before make-process."
+  (cl-letf (((symbol-function 'cj/executable-find-or-warn)
+             (lambda (&rest _) nil))
+            ((symbol-function 'make-process)
+             (lambda (&rest _) (error "make-process must not be called"))))
+    (should-error (cj/--extract-audio-from-video "/x.mp4" "/tmp/y.mp3" #'ignore)
+                  :type 'user-error)))
+
+;;; cj/transcribe-media dispatcher
+
+(ert-deftest test-tx-transcribe-media-audio-routes-directly ()
+  "Normal: audio paths go straight to the transcription worker, no ffmpeg."
+  (let* ((tmp (make-temp-file "cj-tx-aud-" nil ".mp3"))
+         worker-arg ffmpeg-called)
+    (unwind-protect
+        (cl-letf (((symbol-function 'cj/--start-transcription-process)
+                   (lambda (file &rest _) (setq worker-arg file) 'fake-proc))
+                  ((symbol-function 'cj/--extract-audio-from-video)
+                   (lambda (&rest _) (setq ffmpeg-called t))))
+          (cj/transcribe-media tmp))
+      (delete-file tmp))
+    (should (equal worker-arg tmp))
+    (should-not ffmpeg-called)))
+
+(ert-deftest test-tx-transcribe-media-video-extracts-then-transcribes ()
+  "Normal: video paths invoke ffmpeg; on success the extracted audio
+goes through `cj/--start-transcription-process' with a cleanup hint."
+  (let* ((tmp (make-temp-file "cj-tx-vid-" nil ".mp4"))
+         extract-args worker-call)
+    (unwind-protect
+        (cl-letf (((symbol-function 'cj/--extract-audio-from-video)
+                   (lambda (vid out cb)
+                     (setq extract-args (list vid out cb))
+                     ;; Simulate immediate ffmpeg success.
+                     (funcall cb)))
+                  ((symbol-function 'cj/--start-transcription-process)
+                   (lambda (file &rest rest)
+                     (setq worker-call (cons file rest))
+                     'fake-proc)))
+          (cj/transcribe-media tmp))
+      (delete-file tmp))
+    ;; ffmpeg was asked to extract from tmp.
+    (should extract-args)
+    (should (equal (car extract-args) tmp))
+    ;; The temp audio path passed to ffmpeg matches the path passed to
+    ;; the worker -- in other words the extraction output IS what the
+    ;; worker transcribes.
+    (should (equal (nth 1 extract-args) (car worker-call)))
+    ;; The worker got the temp-audio as cleanup-file (so it gets
+    ;; deleted after transcription completes).
+    (should (equal (nth 1 extract-args) (cadr worker-call)))))
+
+(ert-deftest test-tx-transcribe-media-rejects-non-media ()
+  "Error: non-media paths get rejected up front."
+  (should-error (cj/transcribe-media "/notes/readme.txt") :type 'user-error))
+
+;;; Aliases
+
+(ert-deftest test-tx-old-transcribe-audio-aliases-new-media-command ()
+  "Backwards compat: `cj/transcribe-audio' still resolves to the new
+media dispatcher via defalias."
+  (should (eq (symbol-function 'cj/transcribe-audio) 'cj/transcribe-media)))
+
+(ert-deftest test-tx-old-at-point-aliases-new-media-at-point ()
+  "Backwards compat: `cj/transcribe-audio-at-point' still resolves."
+  (should (eq (symbol-function 'cj/transcribe-audio-at-point)
+              'cj/transcribe-media-at-point)))
+
+;;; Keybinding
+
+(ert-deftest test-tx-dired-T-binds-media-at-point ()
+  "Normal: T in dired-mode-map invokes `cj/transcribe-media-at-point'."
+  (require 'dired)
+  (should (eq (lookup-key dired-mode-map (kbd "T"))
+              #'cj/transcribe-media-at-point)))
+
+(provide 'test-transcription-video)
+;;; test-transcription-video.el ends here