Bulk adding videos to youtube playlist (well, at least adding them faster)

I’ve occasionally wanted to add a lot of videos at once to a youtube playlist.

Usually, this is super annoying since it takes a bunch of mouse presses to just added one video, and you can’t even used keyboard shortcuts (like hitting TAB and then enter).


Add videos -> URL -> enter URL -> Add video.

Repeat for each video, and every single one of those requires you to move your mouse around. You have to wait a bit each time too as the page reloads with your new video on it.

I found a shortcut so that it’s annoying, but slightly less annoying. In this method, you open the modal to add a video, then instead of opening and closing the modal, you can just copy-paste-click to add all your videos. Specifically, this adds them to your “watch later” list. Then you can go to your watch later playlist, click “add all to playlist”, and add them to your desired playlist.

A bit convoluted to explain, but really easy in practice, and so much faster than the old process.

Open up the playlist editor as usual, then entire a URL. Click the “clock” icon.

youtube-1The “clock” should change into a “check mark”. Then you can paste in the next URL (without having to exit the modal) and proceed to add all videos.

youtube-2Finally, go to your “watch later” playlist




Note: If your “watch later” list already has a bunch of videos that you want to keep,

  •   you can create a temporary playlist “temp playlist”.
  • Then on your “watch later” list, click the three dots, and add all of the existing videos to the new “temp playlist”.
  • Then, go to edit the “temp playlist” and click the three dots, then click `add all to` and un-check the `watch later` playlist. this will remove the videos from your `Watch Later` playlist

youtube-4After you are done bulk-adding videos to your other playlist (say `cool playlist`), you can uncheck playlist `Watch later` from “add all to” list. This’ll remove the new videos of your list from the `Watch Later` list and leave it empty. Finally, go back to your `temp playlist` and click “add all to” `Watch later`.

Wow, that was a mouthful, but hopefully it should make sense.

Getting started with AprilTags on Ubuntu 16.04

I recently started working with April tags, since they seem cool & you see them all over the place (used as fiducials for robots trying to walk around a somewhat unstructured environment).


the internet fell short (feel free to skip this section)

It was surprisingly hard to find instructions to get started, my search-fu was failing me. My search results turned up the original “official” website from the April Robotics Laboratory at University of Michigan, https://april.eecs.umich.edu/software/apriltag.html

This had no “getting started” instructions on it. Same for the C++ wrapper by a researcher at CSAIL (now a professor who I met at CMU!) https://people.csail.mit.edu/kaess/apriltags

And same for the ROS wrapper around the Apriltags, which also confusingly seems to have several version that may or may not now be the same. http://wiki.ros.org/apriltags_ros and https://github.com/xenobot-dev/apriltags_ros

(oh wait neat, there are instructions at https://cmumrsdproject.wikispaces.com/AprilTags_ROS). However, I’m still not terribly familiar with ROS, so I wasn’t too enthused about using this wrapper.

Fortunately Patrick over at Kuindersma’s lab above me was able to get me started.

getting started

  1. Download and install C++ wrapper as per instructions at https://people.csail.mit.edu/kaess/apriltags/
    See below:
  2. sudo apt-get install subversion cmake libopencv-dev libeigen3-dev libv4l-dev
    sudo port install pkgconfig opencv eigen3
    svn co https://svn.csail.mit.edu/apriltags
    cd apriltags
  3. Yay, now a window pops open (see “troubleshooting” if it doesn’t, as was the case for me) with a video stream. But we need tags for it to recognize!

Getting tags

I actually found this pretty annoying, the zipped files on those sites give you a thousand options and it’s not clear which ones will work. So for me, I actually had my friend give me four tags that definitely work.

ID = #0 #1 #6 and #7 tags.

  1. Print out tag
  2. Run
  3. Now stick the tag in front of your camera. In the videostream you should now see a circle. In the terminal you should now see data streaming out.
  4. The data display shows distance (from the camera to the tag), the xyz location of the center of the tag, as well as the roll, pitch, and yaw. These coordinates will depend on which side you put pointing up when you pasted the tag on, so beware.  In fact, none of the data should be taken as absolute until you calibrate your camera.
2 tags detected: 
Id: 1 (Hamming: 0) distance=0.079741m, x=0.000532, y=0.006102, z=-1.487915, yaw=-0.134615, pitch=0.071828, roll=-0.041146
Id: 7 (Hamming: 0) distance=0.079741m, x=0.000532, y=0.006102, z=-1.487915, yaw=-0.134615, pitch=0.071828, roll=-0.041146
14.9312 fps
Two apriltags
Example output

calibrate camera

I wandered for a while lost in the lands of https://docs.opencv.org/2.4/doc/tutorials/calib3d/camera_calibration/camera_calibration.html

Fortunately, eventually I found my way to a python library that made the whole process super simple. I ignored the above link (to official openCV docs) entirely. Instead, I used the following python package. All I had to do was print out the checkerboard pattern included in the repository, wave it in front of the camera and record a short video, run the python file, and bam! I had the configuration.yaml file I needed.


To get it working, I did have to make sure I had pyyaml installed
 (venv) nrw@earlgrey:$ sudo -H pip install pyyaml --upgrade

This project is super awesome and included an example you can run right away and inspect. The following line, run in the root takes in the video included in the repo (chessboard.avi) and outputs the resulting configuration file to “calibration.yaml”.

(venv) nrw@earlgrey:~/projects/video2calibration$ ./calibrate.py example_input/chessboard.avi calibration.yaml --debug-dir out

At this point I printed out the checkboard pattern included in the repository, put it on a stiff surface, and then opened cheese (you don’t have to use cheese, we just need to record a video).

Then I waved my board around in front of the camera and recorded a short video.



Anyhow, I record ten or fifteen seconds of video. Then I ran

nrw@earlgrey:~/projects/video2calibration$ ./calibrate.py ~/Videos/Webcam/2018-03-26-112657.webm calibration.yaml --debug-dir out

Performing calibration...
 RMS: 0.442700776066
 camera matrix:
 [[ 666.78668352    0.          343.73827809]
 [   0.          665.79103853  227.19081685]
 [   0.            0.            1.        ]]
 distortion coefficients:  [  6.06301194e-02  -1.94620209e-02   1.45555284e-04   1.24410189e-03

Input calibration parameters into source code

Edit into the demo file

nrw@earlgrey:~/projects/apriltags/example$ vi apriltags_demo.cpp

Specifically, we want to change the following section. Note that we are using the definition of the rotation matrix to pull out (from the calibration.yaml output) the focal point and principal point parameters.


  // default constructor
  Demo() :
    // default settiwgs, most can be modified through command line options (see below)
 [...excerpted section...]
    m_tagSize(0.00944), // in meters
    m_fx(667), // in pixels
    m_fy(666), //
    m_px(344), // principal point

Ah! I forgot, we also needed to measure, using a ruler (or calipers), the size of the apriltag in real life. So just measure one of the sides of the tag (which should be square…) and put it inoto m_tagSize. (The width and height should be the size in pixels of the image from the video camera).

Compile and run (use “make clean” if the build fails, then run “make” again)

nrw@earlgrey:~/projects/apriltags/example$ cd ..
nrw@earlgrey:~/projects/apriltags/$ nrw@earlgrey:~/projects/apriltags/example$ make

Then run the program:

nrw@earlgrey:~/projects/apriltags/$ ./build/bin/apriltag_demo

One easy way to double-check whether the camera is roughly calibrated is to physically measure the distance between the camera and the tag, and then compare to the “distance” output in your terminal. Hopefully they match…


The roll, pitch, and yaw are reported in radians. To convert into degrees, multiply by 57.3 (approximately).


A framerate of 17fps or so is totally reasonable, since the apriltags demo is decently compute intensive. I had a problem with lag, where the video ran smoothly but with a significant lag — this may have been a result of me running the entire thing in a virtual machine. Let me know if you don’t have lag!


I had a somewhat frustrating beginning where I couldn’t get the example program to run.

-- Found OpenCV: /opt/ros/lunar (found version "3.3.1")
 framerate (17fps raesonable, but lag???)
 output is in radians
 9.23346 fps
 0 tags detected:
 0 tags detected:
 0 tags detected:
 0 tags detected:
 0 tags detected:
 0 tags detected:
 0 tags detected:
 0 tags detected:
 1 tags detected:
 OpenCV Error: Assertion failed (mtype == type0 || (((((mtype) & ((512 - 1) << 3)) >> 3) + 1) == 1 && ((1 << type0) & fixedDepthMask) != 0)) in create, file /tmp/binarydeb/ros-lunar-opencv3-3.3.1/modules/core/src/matrix.cpp, line 2542
 terminate called after throwing an instance of 'cv::Exception'
 what():  /tmp/binarydeb/ros-lunar-opencv3-3.3.1/modules/core/src/matrix.cpp:2542: error: (-215) mtype == type0 || (((((mtype) & ((512 - 1) << 3)) >> 3) + 1) == 1 && ((1 << type0) & fixedDepthMask) != 0) in function create
Id: 15 (Hamming: 1)Aborted (core dumped)

It turned out that because I had ROS installed, or perhaps also because I installed the “apriltags” ROS wrapper, I was having openCV version conflicts.



nrw@earlgrey:~$ pkg-config --modversion opencv

To solve, I simply had to edit one line in the CMakeLists.txt to force it to use the right version of openCV. I added an “exact required” tag, along with my openCV version (, to the appropriate line.

nrw@earlgrey:~/projects/apriltags$ vi CMakeLists.txt 
(line 14)
find_package(OpenCV EXACT REQUIRED)

Then I ran “make” and

nrw@earlgrey:~/projects/apriltags/$ ./build/bin/apriltag_demo

and the example program worked! Huzzah.

the end.