Making a Video Recording Booth, Part 1: Brainstorming

My friends Jacqui and John got married, and they’ve asked me to provide a video booth/kiosk for their celebration party (in less than three weeks from now, eek!). The idea is that guests will be able to record their own video messages to the bride and groom – essentially a multimedia guestbook. This is very similar to the self-service photo booth, which has become a ‘must-have’ item at weddings and parties, and there are a number of commercial and open source photo booth software solutions available (SparkBooth, PhotoBoof, etc.)

I assumed that there would be similar software available for self-service video recording booths, but my Google-fu has largely failed me here. It seems that most of the software for this use is commercially developed and packaged with turn-key hardware solutions. I don’t have big bucks to spend here, so I won’t be buying/renting a commercial video booth. After much fruitless searching for a suitable product, I’ve determined that I’ll be writing my own video booth software.

My requirements for video booth software:

1. Should have a simple, intuitive and bulletproof user interface. Anyone should be able to record a video without ever having used a computer before (I’m looking at you, Grandma), and the workflow must survive enthusiastic button-mashing by tipsy guests.
2. Should not need expensive hardware (again, tipsy guests). I don’t have a powerful computer available to me for this project. This may be a challenging requirement, as video encoding in software is very CPU-intensive.
3. Should be able to handle continuous use. If there’s a line of people waiting to record a greeting, a guest should be able to begin recording as soon as the previous person has finished their recording. This implies that I’ll either be encoding captured video/audio in real time or using background encoding tasks that are invisible to users, either of which may be a challenge considering my ‘no expensive hardware’ requirement.
4. Should be able to record high quality video. I would hate see once-in-a-lifetime video memories look pixelated and crappy. My cell phone can take good video, so my video booth had better take great video. I’d be happiest with 1920×1080 (1080p HD), and I’d settle for 1280×720 (720p HD). A frame rate of 30FPS is preferable, but I’d go to 24 or 25FPS if needed, and I’d like to keep a data rate around 5000kbps. Absolute worst case scenario: 640×480 (SD) resolution at 24FPS and 500kbps data rate; I refuse to go any lower. I know I’m really challenging myself here, considering the need for cheap hardware and continuous use.

The spare computer that I have available for this project is an Acer Aspire AX1430. It’s got a wimpy little AMD E-450 processor, which is only slightly better than the dual-core Atoms.  The computer has 4GB of RAM, a 500GB HDD, and I’ve replaced the optical drive with a 32GB SSD. It’s essentially a high-end nettop, and doesn’t have much available horsepower for tasks like video encoding.  In order to keep resource usage as light as possible, the machine is running Lubuntu 12.04.

Other hardware that I have available to play with:

• Logitech C260 webcam.
• An Arduino microcontroller.
• Wireless RF keyboard and mouse.
• I’m considering using a Big Red Button for the user interface:

The user experience I have in mind is exceedingly simple:

1. A webcam sits on top of a large monitor, which displays a full-screen preview of the video camera feed at all times. There won’t be a keyboard or mouse available, just a big illuminated red button in front of the monitor. In the idle (waiting) state, a text overlay invites the guest to “Press the button to begin recording.”
2. When a guest presses the button, the text overlay gives them a quick countdown (3…2…1) and then recording begins. An overlay message (maybe including the ubiquitous flashing red circle ‘recording’ symbol) instructs the guest to “Press the button to stop recording.”  The big red button will flash during recording.
3. The guest records their video message and then presses the button to complete their recording. A quick “Thank you!” message flashes, and then we’re back to the idle state, ready for the next person.

There won’t be an Internet connection at the party, so I’m not considering features like streaming video, automated uploading, email notifications, etc. at this time.

For the video capture and encoding backend, it looks like GStreamer is the de-facto choice as far as libraries go. I’ve used Processing to interface with arduino in the past, so I’d like to reuse some of that code (there’s a time crunch here!). There’s an implementation of GStreamer for Processing called GSVideo which seems to have garnered a substantial following, so that may be the best choice for the UX.

Now I’m off to run some GStreamer tests and see if my wimpy little computer will be capable of on-the-fly previewing and encoding of HD video. My suspicion is ‘no’, but I’m ever-hopeful! I’ll follow up soon with those results.

Making an Arduino-controlled Delta Robot

A delta robot is a parallel robot that’s designed for precise and high speed movement of light payloads.  They’re generally used for pick-and-pack operations.  I’ve wanted to build a delta robot since I saw this video, so I took a weekend last summer to put something together as a technology demonstration for the high school robotics club that I coach.

The complete robot

The servos and upper assembly

The upper link of an arm

A delta robot is composed of three two-segment ‘arms’ mounted at 120 degree intervals.  The arms use parallelograms to restrict the motion of the ‘wrist’ and keep it in a static orientation.  For a much better description, check out Wikipedia, and for the math geeks there’s an excellent writeup of delta robot kinematics over at Trossen Robotics.

To build my delta robot I started with three HS-645MG servos, and mounted them on some particle board.  I fabricated upper arms out of Tetrix beam and used some JB-Weld to attach long standoffs perpendicularly at the ends of the arms.  The standoffs hold small ball joints (I used some ball endsthat were intended for RC car suspensions) that will provide the free movement that is required of these joints.  The rods that make up the parallel linkage for the second segment of the arms are aluminum. I bored holes in the ends of these on the lathe and pressed small bolts into the holes to create a mounting point for the ‘cap’ portion of the ball ends.  The lower triangle is just a quick mock up made of Lego with some more long standoffs zip-tied to it to provide mounting points for the ball ends.

On the software side, there are two components.  I modified an excellent Arduino sketch originally created by Bryan at Principia Labs to drive the hardware.  The Arduino sketch uses the Servo.h library to control the three servos.  It listens over a serial connection for three-byte control commands in the format start_byte, servo_number, desired_position where the start_byteis always 255.  Servo number 99 is used as a control channel to enable and disable the servos.  Sending a desired position of 180 to servo 99 will turn all the servos on, and sending position 0 to servo 99 will disable all servos and power them off.

Processing GUI

To control the robot I wrote some software in the Processing language.  I used the really nice ControlP5 GUI library to make text boxes and sliders to control servo positions.  The kinematics of converting three servo angles to a position in XYZ axes and vice-versa is..interesting, to say the least!  Luckily great minds have gone before and completed this math for me, even including C code. Again, Trossen Robotics forums are your friend.

I’m making all the code for the Arduino sketch and the Processing GUI available for download from my Box.net account (Edit: and on GitHub).  The code is well-commented, but I did not originally intend to publish it, so it’s a little rough around the edges.  Feel free to ask any questions in the post comments and I’ll try and clear things up if it’s confusing.

I’ll wrap things up with a quick video of the delta robot in action. Enjoy!