From faf62c69d499934b6de0840b0a6bdc3db4b79994 Mon Sep 17 00:00:00 2001
From: Sacha Chua <sacha@sachachua.com>
Date: Tue, 7 Dec 2021 17:26:55 -0500
Subject: HTML-related functions

---
 emacsconf-html.el | 516 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 516 insertions(+)
 create mode 100644 emacsconf-html.el

diff --git a/emacsconf-html.el b/emacsconf-html.el
new file mode 100644
index 0000000..33c1181
--- /dev/null
+++ b/emacsconf-html.el
@@ -0,0 +1,516 @@
+
+(defcustom conf-media-base-url "https://media.emacsconf.org/" "Base URL for published media files."
+  :type 'string
+  :group 'emacsconf)
+
+(defcustom conf-main-extensions '(".org" ".odp" ".pdf" ".el" "--main.vtt" "--main_fr.vtt" "--main_ja.vtt" "--chapters.vtt" "--main--chapters.vtt")
+  "Extensions to list on public pages."
+  :type '(repeat string)
+  :group 'emacsconf)
+
+(defcustom conf-protected-extensions '(".en.srv2" ".srt")
+  "Extensions to list in the staging area."
+  :group 'emacsconf)
+(defcustom conf-public-media-directory nil "Can be over TRAMP" :type 'string :group 'emacsconf)
+(defcustom conf-protected-media-directory nil "Can be over TRAMP" :type 'string :group 'emacsconf)
+
+(defun conf-index-card (talk &optional extensions)
+  "Format an HTML card for TALK, linking the files  in EXTENSIONS."
+    (let* ((video-slug (plist-get talk :video-slug))
+           (video-file (and (plist-get talk :video-file) (expand-file-name (plist-get talk :video-file) conf-captions-directory)))
+           (video (conf-index-card-video (or (plist-get talk :video-id) "mainVideo") video-file talk extensions)))
+      ;; Add extra information to the talk
+      (setq talk
+            (append
+             talk
+             (list
+              :video-html (plist-get video :video)
+              :chapter-list (or (plist-get video :chapter-list) "")
+              :resources (plist-get video :resources)
+              :extra (or (plist-get talk :extra) "") 
+              :speaker-info (or (plist-get talk :speakers) ""))))
+      (conf-replace-plist-in-string
+       talk
+       "<div class=\"vid\">${video-html}${resources}${extra}${chapter-list}</div>")))
+
+(defun conf-index-card-video (video-id video-file talk extensions)
+  (let* ((wiki-caption-dir (expand-file-name
+                            "captions"
+                            (expand-file-name 
+                             (plist-get talk :conf-year)
+                             conf-directory)))
+         (chapter-info (and video-file
+                            (conf-make-chapter-strings
+                             (expand-file-name
+                              (concat (file-name-base video-file) "--chapters.vtt")
+                              wiki-caption-dir)
+                             (plist-get talk :track-base-url))))
+         (info
+          (append
+           (list
+            :source-src
+            (when video-file
+              (if (plist-get talk :public)
+                  (format "%s%s/%s" conf-media-base-url (plist-get talk :conf-year)
+                          (file-name-nondirectory video-file))
+                (file-name-nondirectory video-file)))
+            :captions
+            (and video-file
+                 (conf-video-subtitle-tracks
+                  (expand-file-name (concat (file-name-base video-file) ".vtt") wiki-caption-dir)
+                  (or (plist-get talk :track-base-url)
+                      (plist-get talk :base-url))))
+            :chapter-track (or (plist-get chapter-info :track) "")
+            :chapter-list (or (plist-get chapter-info :html) "")
+            :video-id video-id
+            :video-duration (if (and video-file (file-exists-p video-file))
+                                (format-seconds "%m:%.2s" (/ (conf-get-file-duration-ms video-file) 1000)))
+            :video-file-size (if (and video-file (file-exists-p video-file))
+                                 (file-size-human-readable (file-attribute-size (file-attributes video-file))))
+            :other-files (mapconcat (lambda (s) (concat "<li>" s "</li>"))
+                                    (conf-link-file-formats-as-list talk (or extensions conf-published-extensions))
+                                    "")
+            :poster (and video-file (format "https://media.emacsconf.org/%s/%s.png" (plist-get talk :conf-year) (file-name-base video-file)))
+            :toobnix-info (if (plist-get talk :toobnix-url)
+                              (format
+                               "<li><a href=\"%s\">View on Toobnix</a></li>"
+                               (plist-get talk :toobnix-url))
+                            ""))
+           
+           talk)))
+    (list
+     
+     :video
+     (conf-replace-plist-in-string
+      info
+      (if (and video-file (file-exists-p video-file))
+          "<video controls preload=\"metadata\" poster=\"${poster}\" id=\"${video-id}\"><source src=\"${source-src}\" />${captions}${chapter-track}</video>"
+        "The video for \"${title}\" will be posted here when available. You can also subscribe to the <a href=\"https://lists.gnu.org/mailman/listinfo/emacsconf-discuss\">emacsconf-discuss mailing list</a> for updates."))
+     :chapter-list (plist-get chapter-info :html)
+     :resources
+     (conf-replace-plist-in-string
+      (append info
+              (list :video-download
+                    (if video-file
+                        (conf-replace-plist-in-string
+                         info
+                         "<li><a href=\"${source-src}\">Download .webm video (${video-duration}, ${video-file-size}B)</a></li>")
+                      "")))
+      "<div class=\"files resources\"><ul>${video-download}${other-files}${toobnix-info}</ul></div>"))))
+
+(when (featurep 'memoize)
+  (memoize #'conf-get-file-duration-ms))
+
+(defun conf-create-talk-pages (conf-info)
+  (interactive (list (conf-get-talk-info)))
+  "Populate year/talks/*.md files.
+These should include the nav and schedule files, which will be
+rewritten as needed.  After they are generated, they should be all
+right to manually edit to include things like additional
+resources."
+  ;; TODO: No longer necessary?
+  (require 's)
+  (mapc (lambda (o)
+          (when (plist-get o :talk-id)
+            (let ((filename (expand-file-name (format "%s.md" (plist-get o :slug))
+                                              (expand-file-name "talks" (expand-file-name conf-year conf-directory)))))
+              (unless (file-exists-p filename)
+                (with-temp-file filename
+                  (let ((meta "!meta")
+                        (title (or (plist-get o :title) ""))
+                        (speakers (or (plist-get o :speakers) ""))
+                        (talk-id (or (plist-get o :talk-id) ""))
+                        (slug (or (plist-get o :slug) ""))
+                        (info (or (plist-get o :info) "")))
+                    (insert
+                     (s-lex-format "[[${meta} title=\"${title}\"]]
+[[${meta} copyright=\"Copyright &copy; ${conf-year} ${speakers}\"]]
+[[!inline pages=\"internal(${conf-year}/info/${slug}-nav)\" raw=\"yes\"]]
+
+<!-- You can manually edit this file to update the abstract, add links, etc. --->\n
+
+# ${title}
+${speakers}
+
+${info}
+
+[[!inline pages=\"internal(${conf-year}/info/${slug}-schedule)\" raw=\"yes\"]]
+
+[[!inline pages=\"internal(${conf-year}/info/${slug}-nav)\" raw=\"yes\"]]
+"))))))))
+        conf-info))
+
+(defun conf-wiki-talk-resources (o)
+  (setq o (append (list :base-url
+                        (concat conf-media-base-url (plist-get o :conf-year) "/")
+                        :track-base-url
+                        (format "/%s/captions/" (plist-get o :conf-year)))
+                  o))
+  (concat
+   (if (plist-get o :qa-public) "# Talk\n\n" "")
+   (conf-index-card o conf-main-extensions)
+   (if (plist-get o :qa-public)
+       (concat "\n\n# Q&A\n\n"
+               (conf-index-card (append
+                                 (list
+                                  :public 1
+                                  :video-id "qanda"
+                                  :toobnix-url nil
+                                  :video-file (expand-file-name
+                                               (concat (file-name-sans-extension (plist-get o :video-slug)) "--answers.webm")
+                                               conf-captions-directory))
+                                 o)
+                                (list "--answers.vtt" "--answers--chapters.vtt")))
+     "")))
+
+
+
+(defun conf-format-talk-schedule-info (o)
+  (let ((friendly (concat "/" conf-year "/talks/" (plist-get o :slug) ))
+        (timestamp (org-timestamp-from-string (plist-get o :scheduled))))
+    (concat
+     "[[!toc  ]]\n"
+
+     (if (plist-get o :q-and-a) (format "Q&A: %s  \n" (plist-get o :q-and-a)) "")
+     (if (member conf-publishing-phase '(program schedule)) (concat "Status: " (plist-get o :status-label) "  \n") "")
+     "Duration: " (or (plist-get o :video-duration)
+                      (concat (plist-get o :duration) " minutes"))
+     "  \n"
+     (if (and (member conf-publishing-phase '(program schedule))
+              (not (member (plist-get o :status) '("DONE" "CANCELLED" "STARTED"))))
+         (let ((start (org-timestamp-to-time (org-timestamp-split-range timestamp)))
+               (end (org-timestamp-to-time (org-timestamp-split-range timestamp t))))
+           (format
+            "<div class=\"times\" start=\"%s\" end=\"%s\">%s<br /><a href=\"/2021/\">Find out how to watch and participate</a></div>"
+            (format-time-string "%Y-%m-%dT%H:%M:%SZ" start t)
+            (format-time-string "%Y-%m-%dT%H:%M:%SZ" end t)
+            (string-join (conf-timezone-strings o) "<br />")))
+       "") 
+     "\n"
+     (if (plist-get o :alternate-apac)
+         (format "[[!inline pages=\"internal(%s/inline-alternate)\" raw=\"yes\"]]  \n" conf-year)
+       "")
+     "\n"
+     "If you have questions and the speaker has not indicated public contact information on this page, please feel free to e-mail us at <emacsconf-submit@gnu.org> and we'll forward your question to the speaker.\n\n"
+     (if (plist-get o :public) (conf-wiki-talk-resources o) "")
+     "\n# Description\n\n")))
+
+(defun conf-generate-schedule-page (talk)
+  (interactive (list (conf-get-talk-info-for-subtree)))
+  (with-temp-file (expand-file-name (format "%s-schedule.md" (plist-get talk :slug))
+                                    (expand-file-name "info" (expand-file-name conf-year conf-directory)))
+    (insert
+     "<!-- Automatically generated by conf-create-info-pages -->\n\n"
+     (conf-format-talk-schedule-info talk) "\n")))
+
+(defun conf-generate-info-pages ()
+  (interactive)
+  "Populate year/info/*-nav and *-schedule.md files."
+  ;; TODO: No longer necessary?
+  (require 's)
+  (let* ((talks (seq-remove (lambda (o) (string= (plist-get o :status) "CANCELLED"))
+                            (conf-filter-talks (conf-get-talk-info))))
+         (next-talks (cdr talks))
+         (prev-talks (cons nil talks)))
+    (while talks
+      (let* ((o (pop talks))
+             (next-talk (conf-format-talk-link (pop next-talks)))
+             (prev-talk (conf-format-talk-link (pop prev-talks)))
+             (friendly (concat "/" conf-year "/talks/" (plist-get o :slug) ))
+             (nav-links (format "Back to the [[schedule]]  \n%s%s"
+                                (if prev-talk (format "Previous: %s  \n" prev-talk) "")
+                                (if next-talk (format "Next: %s  \n" next-talk) ""))))
+        (with-temp-file (expand-file-name (format "%s-nav.md" (plist-get o :slug))
+                                          (expand-file-name "info" (expand-file-name conf-year conf-directory)))
+          (insert nav-links))
+        (conf-generate-schedule-page o)))))
+
+(defun conf-generate-talks-page (conf-info)
+    (interactive "p")
+    (let ((info conf-info))
+      (with-temp-buffer
+        (find-file "talk-details.md")
+        (erase-buffer)
+        (insert (format "<table><thead><th>Duration</th><th>Title</th><th>Speakers</th></thead><tbody>%s</tbody></table>"
+                        (mapconcat
+                         (lambda (o)
+                           (let* ((title (plist-get o :title))
+                                  (speakers (plist-get o :speakers)))
+                             (if (null (plist-get o :talk-id))
+                                 (format "<tr><td colspan=\"3\">%s</td></tr>" (conf-format-talk-link o))
+                               (format "<tr><td>%s</td><td>%s</td><td>%s</td><tr>" 
+                                       (plist-get o :duration)
+                                       (conf-format-talk-link o)
+                                       (plist-get o :speakers)))))
+                         info "\n")))
+        (save-buffer))))
+
+(defun conf-generate-main-schedule (&optional filename)
+  (interactive)
+  (with-temp-file (expand-file-name "schedule-details.md" (expand-file-name conf-year conf-directory))
+    (insert (conf-format-talk-info-as-schedule (conf-get-talk-info)))))
+
+(defun conf-format-talk-link (talk)
+  (and talk (if (plist-get talk :talk-id)
+                (format "<a href=\"/%s/talks/%s\">%s</a>"
+                        conf-year
+                        (plist-get talk :slug)
+                        (plist-get talk :title))
+              (plist-get talk :title))))
+
+
+(defun conf-format-talk-info-as-schedule (info)
+  (let* ((talks (seq-filter
+                 (lambda (o)
+                   (and (not (string= (plist-get o :status) "CANCELLED"))
+                        (plist-get o :speakers)))
+                 (conf-filter-talks info)))
+         (captioned (seq-filter (lambda (o) (plist-get o :captioner)) talks))
+         (cancelled (seq-filter (lambda (o) (string= (plist-get o :status) "CANCELLED")) info))
+         (received (seq-remove (lambda (o) 
+                                 (plist-get o :captioner)) 
+                               talks)))
+    (format "<div>%d talks total: %d captioned (%d min), %d waiting for captions (%d min)</div>
+<table width=\"100%%\">%s%s</table>%s"
+            (length talks)
+            (length captioned)
+            (apply '+ (mapcar (lambda (info) (string-to-number (plist-get info :duration))) captioned))
+            (length received)
+            (apply '+ (mapcar (lambda (info) (string-to-number (plist-get info :duration)))
+                              received))
+            (pcase conf-publishing-phase
+              ('program "<tr><th>Status</th><th>Title<th><th>Speaker(s)</th></tr>")
+              ('schedule "<tr><th>Status</th><th>Start</th><th>Title</th><th>Speaker(s)</th></tr>")
+              ('resources "<tr><th>Title</th><th>Speaker(s)</th><th>Resources</th></tr>")) 
+            (mapconcat
+             (lambda (o)
+               (let* ((time-fmt "%l:%M %p")
+                      (timestamp (org-timestamp-from-string (plist-get o :scheduled)))
+                      (start (if timestamp (format-time-string time-fmt (org-timestamp-to-time (org-timestamp-split-range timestamp))) ""))
+                      (end (if timestamp (format-time-string time-fmt (org-timestamp-to-time (org-timestamp-split-range timestamp t))) ""))
+                      (title (plist-get o :title))
+                      (status (pcase (plist-get o :status)
+                                ("CAPTIONED" "captioned")
+                                ("PREREC_RECEIVED" "received")
+                                ("DONE" "done")
+                                ("STARTED" "now playing")
+                                (_ "")))
+                      (speakers (or (plist-get o :speakers) "")))
+                 (pcase conf-publishing-phase
+                   ('program
+                    (if (eq (plist-get o :type) 'headline)
+                        (format "<tr><td colspan=\"3\"><strong>%s<strong></td></tr>"
+                                (if (plist-get o :slug)
+                                    (conf-format-talk-link o)
+                                  title))
+                      (format "<tr><td>%s</td><td>%s</td><td>%s</td></tr>"
+                              status
+                              (conf-format-talk-link o) speakers)))
+                   ('schedule
+                    (if (eq (plist-get o :type) 'headline)
+                        (format "<tr><td colspan=\"4\"><strong>%s<strong></td></tr>"
+                                (if (plist-get o :slug)
+                                    (conf-format-talk-link o)
+                                  title))
+                      (format "<tr><td>%s</td><td width=100>~%s</td><td>%s</td><td>%s</td></tr>"
+                              status
+                              start (conf-format-talk-link o) speakers)))
+                   ('resources
+                    (if (eq (plist-get o :type) 'headline)
+                        (format "<tr><td colspan=\"3\"><strong>%s<strong></td></tr>"
+                                (if (plist-get o :slug)
+                                    (conf-format-talk-link o)
+                                  title))
+                      (format "<tr><td>%s</td><td>%s</td><td><ul>%s</ul></td></tr>"
+                              (conf-format-talk-link o) speakers
+                              (mapconcat (lambda (s) (concat "<li>" s "</li>"))
+                                         (conf-link-file-formats-as-list
+                                          (append o
+                                                  (list :base-url (format "%s%s/" conf-media-base-url conf-year)))
+                                          (append conf-published-extensions '("--main.webm")))
+                                         "")))))))
+             (seq-remove (lambda (o) (string= (plist-get o :status) "CANCELLED"))
+                         (cdr info))
+             "\n")
+            (if (> (length cancelled) 0)
+                (format "<div class=\"cancelled\">Cancelled:<ul>%s</ul></div>"
+                        (mapconcat (lambda (talk) (format "<li><a href=\"/%s/talks/%s\">%s</a> - %s</li>"
+                                                          conf-year
+                                                          (plist-get talk :slug)
+                                                          (plist-get talk :title)
+                                                          (plist-get talk :speakers)))
+                                   cancelled "\n"))
+              ""))))
+
+(defun conf-timezone-strings (o)
+  (let* ((timestamp (org-timestamp-from-string (plist-get o :scheduled)))
+         (start (org-timestamp-to-time (org-timestamp-split-range timestamp)))
+         (end (org-timestamp-to-time (org-timestamp-split-range timestamp t))))
+    (mapcar
+     (lambda (tz)
+       (format "%s - %s"
+               (format-time-string "%A, %b %e %Y, ~%l:%M %p"
+                                   start tz)
+               (format-time-string "%l:%M %p %Z"
+                                   end tz)))
+     conf-timezones)))
+
+(defun conf-make-protected-index (filename)
+  (interactive (list (expand-file-name "index.html" conf-protected-media-directory))) 
+  (setq conf-info (conf-get-talk-info))
+  (with-temp-file filename
+    (let* ((talks (seq-filter (lambda (o) (plist-get o :video-file)) (conf-filter-talks conf-info)))
+           (received (seq-remove (lambda (o) (plist-get o :captioner)) talks))
+           (captioned (seq-filter (lambda (o) (plist-get o :captioner)) talks)))
+      (insert
+       "<html><meta charset=\"UTF-8\"><body>"
+       (format "<h1>Talks to be captioned (%d minutes)</h1><ul class=\"videos\">"
+               (apply '+ (seq-map (lambda (talk) (string-to-number (plist-get talk :duration)))
+                                  received)))
+       (mapconcat
+        (lambda (f)
+          (format  "<li><strong>%s</strong><br />%s<br />%s</li>"
+                  (plist-get f :title)
+                  (plist-get f :speakers)
+                  (conf-index-card
+                   (append
+                    f
+                    (list :extra
+                          (if (plist-get f :caption-note) (concat "<div class=\"caption-note\">" (plist-get f :caption-note) "</div>") "")))
+                   (append conf-main-extensions conf-protected-extensions))))
+        received
+        "\n")
+       (format
+        "</ul><h1>%d captioned talks ready for enjoyment (%d minutes)</h1>"
+        (length captioned)
+        (apply '+ (seq-map (lambda (talk) (string-to-number (plist-get talk :duration))) captioned)))
+       "<ol class=\"videos\">"
+       (mapconcat (lambda (f) (format "<li><strong>%s</strong><br />%s<br />%s</li>"
+                                      (plist-get f :title)
+                                      (plist-get f :speakers)
+                                      (conf-index-card f conf-main-extensions)))
+                  captioned "\n")
+       "</ol>"
+       (if (file-exists-p (expand-file-name "include-in-index.html" conf-captions-directory))
+           (with-temp-buffer (insert-file-contents (expand-file-name "include-in-index.html" conf-captions-directory)) (buffer-string))
+         "")
+       "</body></html>"))))
+
+(defun conf-make-public-index (filename)
+  (interactive (list (expand-file-name "index.html" conf-public-media-directory))) 
+  (setq conf-info (conf-get-talk-info))
+  (with-temp-file filename
+    (insert
+     "<html><body>"
+     "<h1>" conf-name " " conf-year "</h1>"
+     "<div class=\"m3u\"><a href=\"index.m3u\">M3U playlist for playing in MPV and other players</a></div>"
+     "<ol class=\"videos\">"
+     (mapconcat (lambda (f) (format "<li>%s</li>" (conf-index-card f '(".org" ".pdf" "--main.vtt"))))
+                (conf-public-talks conf-info)
+                "\n")
+     "</ol>"
+     (if (file-exists-p (expand-file-name "include-in-index.html" conf-captions-directory))
+         (with-temp-buffer (insert-file-contents (expand-file-name "include-in-index.html" conf-captions-directory)) (buffer-string))
+       "")
+     "</body></html>")))
+
+(defun conf-make-public-index-on-wiki ()
+  (interactive)
+  (let ((info (seq-filter (lambda (o)
+                            (not (string= (plist-get o :status) "CANCELLED")))
+                          (conf-filter-talks (conf-get-talk-info)))))
+    (with-temp-file (expand-file-name "all-include.md" (expand-file-name conf-year conf-directory))
+      (insert
+       "<ol class=\"videos\">"
+       (mapconcat
+        (lambda (f)
+          (format "<li><div class=\"title\"><a href=\"%s\">%s</a></div><div class=\"speakers\">%s</div>%s%s</li>"
+                  (plist-get f :url)
+                  (plist-get f :title)
+                  (or (plist-get f :speakers) "")
+                  (if (plist-get f :public)
+                      (conf-index-card
+                       (append (list :base-url
+                                     (concat conf-media-base-url (plist-get f :conf-year) "/")
+                                     :track-base-url
+                                     (format "/%s/captions/" (plist-get f :conf-year)))
+                               f)
+                       conf-published-extensions)
+                    "")
+                  (if (plist-get f :qa-public)
+                      (conf-index-card
+                       (append
+                        (list
+                         :public 1
+                         :base-url (concat conf-media-base-url (plist-get f :conf-year) "/")
+                         :video-id "qanda"
+                         :track-base-url
+                         (format "/%s/captions/" (plist-get f :conf-year))
+                         :video-file (expand-file-name
+                                      (concat (file-name-sans-extension (plist-get f :video-slug)) "--answers.webm")
+                                      conf-captions-directory))
+                        f)
+                       (list "--answers.vtt" "--answers--chapters.vtt"))
+                    "")))
+        info "\n"))
+       "</ol>")))
+
+
+
+(defun conf-make-chapter-strings (filename track-base-url)
+  (when (file-exists-p filename)
+    (let ((chapters (with-temp-buffer
+                      (insert-file-contents filename)
+                      (subed-vtt--init)
+                      (conf-chapters-buffer-as-list))))
+      (list
+       :track (format "<track kind=\"chapters\" label=\"Chapters\" src=\"%s\"\" />"
+                      (concat (or track-base-url "") (file-name-nondirectory filename)))
+       :html (format "<ol class=\"chapters\">\n%s\n</ol>"
+                     (mapconcat
+                      (lambda (chapter)
+                        (format "<li data-start=\"%.3f\" data-stop=\"%.3f\">%s %s</li>"
+                                (/ (plist-get chapter :start-ms) 1000.0)
+                                (/ (plist-get chapter :stop-ms) 1000.0)
+                                (format-seconds "%.2h:%z%.2m:%.2s" (floor (/ (plist-get chapter :start-ms) 1000)))
+                                (plist-get chapter :text)))
+                      chapters
+                      "\n"))))))
+
+(defun conf-video-subtitle-tracks (filename track-base-url)
+  (concat
+   (if (file-exists-p filename)
+       (format "<track label=\"English\" kind=\"captions\" srclang=\"en\" src=\"%s\" default />"
+               (concat (or track-base-url "") (file-name-nondirectory filename)))
+     "")
+   (mapconcat
+    (lambda (lang)
+      (let ((lang-file (concat (file-name-sans-extension filename) "_" (car lang) (file-name-extension filename))))
+        (if (file-exists-p lang-file)
+            (format "<track label=\"%s\" kind=\"captions\" srclang=\"%s\" src=\"%s--main_%s.vtt\" />"
+                    (cdr lang)
+                    (car lang)
+                    (concat (or track-base-url "") (file-name-nondirectory lang-file))
+                    (car lang))
+          "")))
+    '(("fr" . "French") ("ja" . "Japanese"))
+    "")))
+
+(defun conf-link-file-formats (video-slug extensions)
+  (string-join (conf-link-file-formats-as-list video-slug extensions) " "))
+
+(defun conf-link-file-formats-as-list (talk extensions)
+  (let ((video-slug (plist-get talk :video-slug))
+        (wiki-captions-dir (expand-file-name "captions" (expand-file-name (plist-get talk :conf-year) conf-directory))))
+    (delq nil (seq-map (lambda (ext)
+                         (if (file-exists-p
+                              (expand-file-name
+                               (concat video-slug ext)
+                               (if (string-match "\\.vtt$" ext)
+                                   wiki-captions-dir
+                                 conf-captions-directory)))
+                             (format "<a href=\"%s%s\">Download %s</a>"
+                                     (or (plist-get talk :base-url) "")
+                                     (concat video-slug ext)
+                                     ext)))
+                       extensions))))
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