Project Overview

Stop Motion @ Jerusalem Film Festival

• Stop motion stations designed for children
• Hardware by Gil Adam and Jonathan Ward

Stop Motion

Stop Motion

Block Diagrams

Stop Motion Stations

High Level Overview

Stop Motion Stations

Raspberry Pi Stations

• Simple image-based UI
  • GTK? Kivy? QT? Finally, Tk
• Receive GPIO commands
  • pigpiod
• Capture camera frames
  • picamera

System

• Arch Linux ARM
  • Customizable
  • Lightweight (raspbian is bloated)
• systemd units for running daemons
• systemd for network connections
• Auto-login && startx
  • via ~/.bash_profile
  • should have used systemd but was lazy

Image-based UI

API

• Movie package
  • frames 0000.jpg, 0001.jpg, ....
  • MANIFEST
  • (NO)PUBLISH flag
• rsync all files to big screen unit for processing
• done

Scalability

• How do we preview at 10 frames per second?
  • Low res thumbnails - in memory
  • High res preview - overlay feh slideshow
• Long running UI process
  • Check carefully for memory leaks!
  • Worst case - process dies and restarts

Big Screen Processing

Processing Unit

• Receive movie packages
• Process *.JPG -> MP4
• Display on central screen

Processing Unit

• Odroid XU4
• 2 x quad core ARM
• 2GB RAM, Mali ARM GPU
• $80

Processing Flow

• Python-based daemon
• Watch for incoming movie packages
• ffmpeg
  • compile 4 second title frame
  • compile 10fps movie
  • concat title + movie
• upload final assets to S3
• mpv
  • control via UNIX socket commands

Scalability

• compile movies
• maintain a smooth display on TV
• ffmpeg is a monster, limit threads

Network

Router

• TP-Link WDR4300
• OpenWrt
  • Open source Linux firmware for routers
• Uplink via 4G netstick
• WLAN coverage for all devices

Tunneling

• Remote access for maintenance and debugging
• Dynamic DNS good enough on landline
  • No good on 4G
• OpenVPN tunnel
  • Use local server for reduced latency
• Map chosen ports -> 22 on each device
  • 2200X > 10.0.0.X:22

Security

• Enable SSH only from VPN/LAN, or:
• Disable password login (key-based ONLY)
  • or you will get scanned and pwned
• Leave no port open #IoT

Website

Website

• Display all movies created each day
• http://stopmo.jff.org.il/

Website

• Simple Flask application
• Pull metadata from S3
• Stash into Redis
• All movies are served directly from S3
  • in-browser or downloaded
• Deployed on Heroku

Poor Man's Background Task

@app.after_request
def update_data(response):
    try:
        if not redis.get('fresh'):
            redis.setex('fresh', 'yes', 60)
            run_expensive_update_operation()
    except ConnectionError as e:
        if app.debug:
            run_expensive_update_operation()
    return response

Full stack

• Prepare to take care of everything
• 'Secondary' tasks are now high-priority
  • Logging
  • Security
  • Debugging
• Performance and scalability
  • know your hardware