tAdd screencasts post - adamsgaard.dk - my academic webpage
(HTM) git clone git://src.adamsgaard.dk/adamsgaard.dk
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---
(DIR) commit 21ba4444566d0ae4e5ad48dab4b2a014d5c296fb
(DIR) parent 0751ae67a20ec95e7264ad43bf95ef53f5e07d9c
(HTM) Author: Anders Damsgaard <anders@adamsgaard.dk>
Date: Tue, 17 Mar 2020 11:11:50 +0100
Add screencasts post
Diffstat:
M Makefile | 3 +--
M ideas.txt | 4 ++--
A pages/004-screencasts.cfg | 7 +++++++
A pages/004-screencasts.html | 112 +++++++++++++++++++++++++++++++
A pages/004-screencasts.txt | 97 ++++++++++++++++++++++++++++++
5 files changed, 219 insertions(+), 4 deletions(-)
---
(DIR) diff --git a/Makefile b/Makefile
t@@ -2,7 +2,6 @@ default: generate
output = output/
-# w3m -dump -T text/html
generate:
mkdir -p $(output)
saait `ls -1r pages/*.cfg`
t@@ -15,7 +14,7 @@ generate:
done
sed -i 's,|\([A-Za-z-]*\)\.html|server|port,|/\1.txt|server|port,' $(output)/index.gph
cp style.css print.css $(output)/
- rsync -rav --progress \
+ rsync -ra \
$(output)/ \
pages/*.txt \
/var/gopher/
(DIR) diff --git a/ideas.txt b/ideas.txt
t@@ -1,5 +1,5 @@
- Gopherhole setup
-- Desktop setup
-- Lego processor
+- Git hosting and stagit
+- Lego film processor
- Granular.jl: Modeling sea ice with particles
- sphere: Requirements and examples
(DIR) diff --git a/pages/004-screencasts.cfg b/pages/004-screencasts.cfg
t@@ -0,0 +1,7 @@
+filename=screencasts.html
+title=Recording screencasts and lectures on OpenBSD and Linux
+description=A quick tip for remote lecturing
+id=screencasts
+tags=teaching, ffmpeg, openbsd
+created=2020-03-17
+updated=2020-03-17
(DIR) diff --git a/pages/004-screencasts.html b/pages/004-screencasts.html
t@@ -0,0 +1,112 @@
+<p>On Monday 2020-03-16 the buildings of the danish public
+sector were closed as an emergency response to COVID-19. This
+includes Aarhus University where I teach two undergraduate courses.
+The university asks lecturers to move their teaching to digital
+platforms. As many times before, this requires creative thinking
+for those of us who do not use Microsoft and Apple products.</p>
+
+<p>I needed a way to record my pdf slideshows while talking over
+the presentation. Ideally, I also wanted the ability to show the
+video of my webcam as an overlay in an attempt to make the presentation
+a bit more engaging when explaining more complex parts.</p>
+
+<p>Fortunately, <a href="https://ffmpeg.org">ffmpeg(1)</a> makes
+it easy to record the screen and laptop audio. I want to keep the
+fan noise low during recording by applying minimal compression and
+encoding. The following shell script serves the purpose of starting
+and stopping recording:</p>
+
+<pre><code>#!/bin/sh
+lockfile=/tmp/screenrecord.pid
+
+startrecording() {
+ out="$HOME/tmp/screenrecord-$(date '+%Y-%m-%d_%H:%M:%S').mkv"
+ ffmpeg -y \
+ -f x11grab \
+ -framerate 60 \
+ -s "$(xdpyinfo | grep dimensions | awk '{print $2}')" \
+ -i $DISPLAY \
+ -f sndio -i default \
+ -r 30 \
+ -c:v libx264rgb -crf 0 -preset ultrafast -c:a flac \
+ "$out" >/dev/null 2>&1 &
+ printf '%s' "$!" > "$lockfile"
+
+ sleep 1
+ if [ ! -f "$out" ]; then
+ echo 'error: ffmpeg recording did not start' >&2
+ notify-send -u CRITICAL "${0##*/}" 'ffmpeg recording did not start'
+ rm -f "$lockfile"
+ exit 1
+ fi
+}
+
+stoprecording() {
+ kill "$(cat "$lockfile")"
+ rm -f "$lockfile"
+ notify-send "${0##*/}" 'recording ended'
+}
+
+if [ -f "$lockfile" ]; then
+ stoprecording
+else
+ startrecording
+fi
+</code></pre>
+
+<p>On Linux systems, the sound driver <b>sndio</b> should be replaced
+by <b>alsa</b> in the above ffmpeg(1) command. I have bound the
+above script to the key binding Alt+r which makes it easy to start
+and stop recording in my X session.</p>
+
+<p>On OpenBSD I can show the webcam video feed with the <a
+href="https://man.openbsd.org/man1/video.1">video(1)</a> command.
+The following script toggles the video feed:<p>
+
+<pre><code>#!/bin/sh
+# remember to `chown $USER /dev/video0`
+if pgrep video >/dev/null 2>&1; then
+ pkill video
+else
+ nohup video -s 320 >/dev/null 2>&1 &
+fi
+</code></pre>
+
+<p>On Linux, the command <strong>mpv /dev/video0</strong> can take
+place of the video(1) command above. I have the above script bound
+to the keybinding Alt+v so I can quickly show and hide my face while
+recording.</p>
+
+<p>When I am done recording a lecture, I encode and compress the
+video file to save bandwidth during upload. The following script
+encodes all input files and reduces file size to roughly 15% without
+concievable loss in quality:</p>
+
+<pre><code>#!/bin/sh
+
+encode() {
+ ffmpeg -y -i "$1" \
+ -c:v libx264 -threads 0 -preset faster -pix_fmt yuv420p \
+ -c:a aac -crf 10 \
+ "${1%%.*}_out.mp4"
+}
+
+for f in "$@"; do
+ encode "$f"
+done
+</code></pre>
+
+<figure class="pagefigure">
+ <video poster="video/screencast.jpg"
+ controls preload="none" class="mediaframe">
+ <source src="video/screencast.webm" type="video/webm">
+ <source src="video/screencast.ogv" type="video/ogg">
+ <source src="video/screencast.mp4" type="video/mp4">
+ <a href="video/screencast.mp4">Link</a>
+ </video>
+ <figcaption>
+ Example screen recording using ffmpeg(1) and video(1)
+ with the above scripts.
+ </figcaption>
+</figure>
+
(DIR) diff --git a/pages/004-screencasts.txt b/pages/004-screencasts.txt
t@@ -0,0 +1,97 @@
+On Monday 2020-03-16 the buildings of the danish public sector were closed as
+an emergency response to COVID-19. This includes Aarhus University where I
+teach two undergraduate courses. The university asks lecturers to move their
+teaching to digital platforms. As many times before, this requires creative
+thinking for those of us who do not use Microsoft and Apple products.
+
+I needed a way to record my pdf slideshows while talking over the presentation.
+Ideally, I also wanted the ability to show the video of my webcam as an overlay
+in an attempt to make the presentation a bit more engaging when explaining more
+complex parts.
+
+Fortunately, [1]ffmpeg(1) makes it easy to record the screen and laptop audio.
+I want to keep the fan noise low during recording by applying minimal
+compression and encoding. The following shell script serves the purpose of
+starting and stopping recording:
+
+#!/bin/sh
+lockfile=/tmp/screenrecord.pid
+
+startrecording() {
+ out="$HOME/tmp/screenrecord-$(date '+%Y-%m-%d_%H:%M:%S').mkv"
+ ffmpeg -y \
+ -f x11grab \
+ -framerate 60 \
+ -s "$(xdpyinfo | grep dimensions | awk '{print $2}')" \
+ -i $DISPLAY \
+ -f sndio -i default \
+ -r 30 \
+ -c:v libx264rgb -crf 0 -preset ultrafast -c:a flac \
+ "$out" >/dev/null 2>&1 &
+ printf '%s' "$!" > "$lockfile"
+
+ sleep 1
+ if [ ! -f "$out" ]; then
+ echo 'error: ffmpeg recording did not start' >&2
+ notify-send -u CRITICAL "${0##*/}" 'ffmpeg recording did not start'
+ rm -f "$lockfile"
+ exit 1
+ fi
+}
+
+stoprecording() {
+ kill "$(cat "$lockfile")"
+ rm -f "$lockfile"
+ notify-send "${0##*/}" 'recording ended'
+}
+
+if [ -f "$lockfile" ]; then
+ stoprecording
+else
+ startrecording
+fi
+
+On Linux systems, the sound driver sndio should be replaced by alsa in the
+above ffmpeg(1) command. I have bound the above script to the key binding Alt+r
+which makes it easy to start and stop recording in my X session.
+
+On OpenBSD I can show the webcam video feed with the [2]video(1) command. The
+following script toggles the video feed:
+
+#!/bin/sh
+# remember to `chown $USER /dev/video0`
+if pgrep video >/dev/null 2>&1; then
+ pkill video
+else
+ nohup video -s 320 >/dev/null 2>&1 &
+fi
+
+On Linux, the command mpv /dev/video0 can take place of the video(1) command
+above. I have the above script bound to the keybinding Alt+v so I can quickly
+show and hide my face while recording.
+
+When I am done recording a lecture, I encode and compress the video file to
+save bandwidth during upload. The following script encodes all input files and
+reduces file size to roughly 15% without concievable loss in quality:
+
+#!/bin/sh
+
+encode() {
+ ffmpeg -y -i "$1" \
+ -c:v libx264 -threads 0 -preset faster -pix_fmt yuv420p \
+ -c:a aac -crf 10 \
+ "${1%%.*}_out.mp4"
+}
+
+for f in "$@"; do
+ encode "$f"
+done
+
+[3]Example screen recording using ffmpeg(1) and video(1) with the above
+scripts.
+
+References:
+
+[1] https://ffmpeg.org/
+[2] https://man.openbsd.org/man1/video.1
+[3] https://adamsgaard.dk/video/screencast.mp4