/cs2030s-2122s1

Primary LanguageJava

Screen Recording with ffmpeg

In case of online exam

Assuming you have no problems installing ffmpeg, here's how you should go about settings so that you can use it reliably on the day of the exam.

  1. Check the video devices configuration by running

    ffmpeg -f avfoundation -list_devices true -i ""

    You should see this section in the output:

    [AVFoundation indev @ 0x7fee71414300] AVFoundation video devices:
[AVFoundation indev @ 0x7fee71414300] [0] NeuralCam Live
[AVFoundation indev @ 0x7fee71414300] [1] FaceTime HD Camera (Built-in)
[AVFoundation indev @ 0x7fee71414300] [2] Capture screen 0

    You should only have one screen during the exam, so you should only see one "Capture screen 0". So, 2 is the label for recording your screen.

  2. Create an alias to for fast screen recording.

    Add this line to your ~/.zshrc or ~/.bashrc using vim:

    alias recordscr='ffmpeg -f avfoundation -r 1 -probesize 20M -threads 1 -i "2:none" -vcodec libx264 -b:v 128k -s hd720'

    :wq and source the file.

  3. Test it!

    $ recordscr test.mp4

    Play it back to see if it's recording the correct thing.

Useful Vim and JShell commands

How to do Lab 1 like a pro?

  1. We read through the entire problem statement and notice we need 2 java and 1 jsh file.

  2. Automatically create the required files and have them in tab view using one single command.

    vim -p Point.java Circle.java maxDiscCoverage.jsh

  3. Use gt to move to the right tab, gT to move left.

  4. Saving files

    Action Keystroke
    Save current file :w
    Save current file and quit :wq OR :x OR ZZ
    Quit current file without saving :q!
    Save all files (that are opened in multiple tabs) :wa
    Save all files and quit :wqa
    Quit all files without saving any :qa!

    *Note: If a new file is empty, it will not be created the first time you try to save it. For that you will need

    touch emptyfile

  5. I want to create another file, how to do it without leaving vim?

    :tabnew AnotherClass.java

  6. I want to open all my existing java files into tabs immediately!

    vim -p *.java

Testing with JShell

jshell> /open Point.java 

jshell> /open Circle.java 

jshell> /open maxDiscCoverage.jsh 

jshell> Point[] points = new Point[]{new Point(0, 0), new Point(1, 0)}
points ==> Point[2] { point (0.000, 0.000), point (1.000, 0.000) }

jshell> findMaxDiscCoverage(points)
$.. ==> 2

jshell> points = new Point[]{new Point(0, -1), new Point(1, 0),
   ...> new Point(0, 1), new Point(-1, 0)}
points ==> Point[4] { point (0.000, -1.000), point (1.000, 0 ... ), point (-1.000, 0.000) }

jshell> findMaxDiscCoverage(points)
$.. ==> 4

jshell> /exit

You probably saw this in the Level 5 jshell testcase which was not readily provided to you as a jsh file. You can make your own level5.jsh by removing all the jshell> in vim. Then, you can automate testing using:

jshell < level5.jsh

Notice the tests always begin with the /open command, if you don't load your classes in order (superclass before subclass), things may go wrong that was not a result of an error in your code but rather JShell misunderstanding your input.

You can do testing without the hassle of typing out any jshell commands like this:

Your level5.jsh will now look like this without the extra commands:

Point[] points = new Point[]{new Point(0, 0), new Point(1, 0)}
findMaxDiscCoverage(points)
points = new Point[]{new Point(0, -1), new Point(1, 0), new Point(0, 1), new Point(-1, 0)}
findMaxDiscCoverage(points)
jshell *.java maxDiscCoverage.jsh < level5.jsh

  • Link to the official course repository, where you earn participation through contributions to Issues and Wiki, the instructions are pretty comprehensive on how to setup your local environment!

  • Always take note of LumiNUS Announcements for updates!

Useful resources:

(Insecure) Shortcut for easy ssh and scp

  1. Download wrapper into the directory you want.

  2. chmod +x wrapper

  3. Usage

    ./wrapper <password> ssh <server>
./wrapper <password> scp <source> <destination>

  4. Create alias in ~/.bashrc or ~/.zshrc file

    alias cs2030ssh="./wrapper myPassword ssh e1234567@stu.comp.nus.edu.sg"
alias cs2030scp="./wrapper myPassword scp"

  5. Restart terminal or source your configuration file.

Note: This cannot be deployed within stu.comp.nus.edu.sg. If you need this to work with your plab account, you would need to use the SoC VPN.