EmacsConf backstage: Using TRAMP and timers to run two tracks semi-automatically
| emacs, emacsconf, org
In previous years, organizers streamed the video feeds for EmacsConf
from their own computers to the Icecast server, which was a little
challenging because of CPU load. A server shared by a volunteer had a
6-core Intel Xeon E5-2420 with 48 GB of RAM, which turned out to be
enough horsepower to run OBS for both the general and development
track for EmacsConf 2022. One of the advantages of this setup was that
I could write some Emacs Lisp to automatically play recorded intros
and talk videos at scheduled times, right from the large Org file that
had all the conference details. I used SCHEDULED: properties to
indicate when talks should play, and that was picked up by another
function that took the Org entry properties and put them into a plist.
This function scheduled the timers:
emacsconf-stream-schedule-timers
(defun emacsconf-stream-schedule-timers (&optional info) "Schedule PLAYING for the rest of talks and CLOSED_Q for recorded talks." (interactive) (emacsconf-stream-cancel-all-timers) (setq info (emacsconf-prepare-for-display (emacsconf-filter-talks (or info (emacsconf-get-talk-info))))) (let ((now (current-time))) (mapc (lambda (talk) (when (and (time-less-p now (plist-get talk :start-time))) (emacsconf-stream-schedule-talk-status-change talk (plist-get talk :start-time) "PLAYING" `(:title (concat "Starting " (plist-get talk :slug))))) (when (and (plist-get talk :video-file) (plist-get talk :qa-time) (not (string-match "none" (or (plist-get talk :q-and-a) "none"))) (null (plist-get talk :stream-files)) ;; can't tell when this is (time-less-p now (plist-get talk :qa-time))) (emacsconf-stream-schedule-talk-status-change talk (plist-get talk :qa-time) "CLOSED_Q" `(:title (concat "Q&A for " (plist-get talk :slug) " (" (plist-get talk :q-and-a) ")")))) ) info)))
It turns out that TRAMP doesn't like being called from timers if there's a chance that two TRAMP processes might run at the same time. I got "Forbidden reentrant call of Tramp" errors when that happened. There was an easy fix, though. I adjusted the schedules of the talks so that they started at least a minute apart.
Sometimes I wanted to cancel just one timer:
emacsconf-stream-cancel-timer
(defun emacsconf-stream-cancel-timer (id) "Cancel a timer by ID." (interactive (list (completing-read "ID: " (lambda (string pred action) (if (eq action 'metadata) `(metadata (display-sort-function . ,#'identity)) (complete-with-action action (sort (seq-filter (lambda (o) (and (timerp (cdr o)) (not (timer--triggered (cdr o))))) emacsconf-stream-timers) (lambda (a b) (string< (car a) (car b)))) string pred)))))) (when (timerp (assoc-default id emacsconf-stream-timers)) (cancel-timer (assoc-default id emacsconf-stream-timers)) (setq emacsconf-stream-timers (delq (assoc id emacsconf-stream-timers) (seq-filter (lambda (o) (and (timerp (cdr o)) (not (timer--triggered (cdr o))))) emacsconf-stream-timers)))))
and schedule just one timer manually:
emacsconf-stream-schedule-talk-status-change
(defun emacsconf-stream-schedule-talk-status-change (talk time new-status &optional notification) "Schedule a one-off timer for TALK at TIME to set it to NEW-STATUS." (interactive (list (emacsconf-complete-talk-info) (read-string "Time: ") (completing-read "Status: " (mapcar 'car emacsconf-status-types)))) (require 'diary-lib) (setq talk (emacsconf-resolve-talk talk)) (let* ((converted (cond ((listp time) time) ((timer-duration time) (timer-relative-time nil (timer-duration time))) (t ; HH:MM (date-to-time (concat (format-time-string "%Y-%m-%d" nil emacsconf-timezone) "T" (string-pad time 5 ?0 t) emacsconf-timezone-offset))))) (timer-id (concat (format-time-string "%m-%dT%H:%M" converted) "-" (plist-get talk :slug) "-" new-status))) (emacsconf-stream-cancel-timer timer-id) (add-to-list 'emacsconf-stream-timers (cons timer-id (run-at-time time converted #'emacsconf-stream-update-talk-status-from-timer talk new-status notification)))))
The actual playing of talks happened using functions that were called
from org-after-todo-state-change-hook. I wrote a function that
extracted the talk information and then called my own list of
functions.
emacsconf-org-after-todo-state-change
(defun emacsconf-org-after-todo-state-change () "Run all the hooks in `emacsconf-todo-hooks'. If an `emacsconf-todo-hooks' entry is a list, run it only for the tracks with the ID in the cdr of that list." (let* ((talk (emacsconf-get-talk-info-for-subtree)) (track (emacsconf-get-track (plist-get talk :track)))) (mapc (lambda (hook-entry) (cond ((symbolp hook-entry) (funcall hook-entry talk)) ((member (plist-get track :id) (cdr hook-entry)) (funcall (car hook-entry) talk)))) emacsconf-todo-hooks)))
For example, this function played the recorded intro and the talk:
emacsconf-stream-play-talk-on-change
(defun emacsconf-stream-play-talk-on-change (talk) "Play the talk." (interactive (list (emacsconf-complete-talk-info))) (setq talk (emacsconf-resolve-talk talk)) (when (or (not (boundp 'org-state)) (string= org-state "PLAYING")) (if (plist-get talk :stream-files) (progn (emacsconf-stream-track-ssh talk "overlay" (plist-get talk :slug)) (emacsconf-stream-track-ssh talk (append (list "nohup" "mpv") (split-string-and-unquote (plist-get talk :stream-files)) (list "&")))) (emacsconf-stream-track-ssh talk (cons "nohup" (cond ((and (plist-get talk :recorded-intro) (plist-get talk :video-file)) ;; recorded intro and recorded talk (message "should automatically play intro and recording") (list "play-with-intro" (plist-get talk :slug))) ;; todo deal with stream files ((and (plist-get talk :recorded-intro) (null (plist-get talk :video-file))) ;; recorded intro and live talk; play the intro and join BBB (message "should automatically play intro; join %s" (plist-get talk :bbb-backstage)) (list "intro" (plist-get talk :slug))) ((and (null (plist-get talk :recorded-intro)) (plist-get talk :video-file)) ;; live intro and recorded talk, show slide and use Mumble; manually play talk (message "should show intro slide; play %s afterwards" (plist-get talk :slug)) (list "intro" (plist-get talk :slug))) ((and (null (plist-get talk :recorded-intro)) (null (plist-get talk :video-file))) ;; live intro and live talk, join the BBB (message "join %s for live intro and talk" (plist-get talk :bbb-backstage)) (list "bbb" (plist-get talk :slug)))))))))
and this function handled IRC announcements when the talk state changed:
emacsconf-erc-announce-on-change
(defun emacsconf-erc-announce-on-change (talk) "Announce talk." (let ((func (pcase org-state ("PLAYING" #'erc-cmd-NOWPLAYING) ("CLOSED_Q" #'erc-cmd-NOWCLOSEDQ) ("OPEN_Q" #'erc-cmd-NOWOPENQ) ("UNSTREAMED_Q" #'erc-cmd-NOWUNSTREAMEDQ) ("TO_ARCHIVE" #'erc-cmd-NOWDONE)))) (when func (funcall func talk))))
The actual announcements were handled by something like this:
erc-cmd-NOWCLOSEDQ
(defun erc-cmd-NOWCLOSEDQ (talk) "Announce TALK has started Q&A, but the host has not yet opened it up." (interactive (list (emacsconf-complete-talk-info))) (when (stringp talk) (setq talk (or (emacsconf-find-talk-info talk) (error "Could not find talk %s" talk)))) (if (emacsconf-erc-recently-announced (format "-- Q&A beginning for \"%s\"" (plist-get talk :slug))) (message "Recently announced, skipping") (emacsconf-erc-with-channels (list (concat "#" (plist-get talk :channel))) (erc-send-message (format "-- Q&A beginning for \"%s\" (%s) Watch: %s Add notes/questions: %s" (plist-get talk :title) (plist-get talk :qa-info) (plist-get talk :watch-url) (plist-get talk :pad-url)))) (emacsconf-erc-with-channels (list emacsconf-erc-hallway emacsconf-erc-org) (erc-send-message (format "-- Q&A beginning for \"%s\" in the %s track (%s) Watch: %s Add notes/questions: %s . Chat: #%s" (plist-get talk :title) (plist-get talk :track) (plist-get talk :qa-info) (plist-get talk :watch-url) (plist-get talk :pad-url) (plist-get talk :channel))))))
All that code meant that during the actual conference, my role was mostly just worrying, and occasionally starting up the Q&A (if I wasn't sure if the code would do it right). The shell scripts I wrote made it easy for the other organizers to take over the second part as they saw how it worked.
Yay timers, Emacs, and TRAMP!
You can find the latest versions of these functions in the emacsconf-el repository.