pi-cam-looper.py

#!/usr/bin/env python

import RPi.GPIO as GPIO
import picamera
import subprocess

# Set up a pin on the GPIO connector for the "record" button.
# We'll use pin 18, which is here:
#
# ....X........
# .............
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.IN, pull_up_down=GPIO.PUD_UP)
#
# Because we set it to "PUD_UP", it's "pulled-up" to a high voltage most of
# the time. To activate it, we'll use a button to short it to ground, which
# is here (among other places):
#
# .X...........
# .............
#
# So wire a button between those two pins and you're all set.

print "Waiting for button push..."
while True:
    # Check the voltage on pin 18 (it's high most of the time).
    high_voltage_on_pin_18 = GPIO.input(18)
    
    # But if someone pushes the button, pin 18 will be shorted to ground.
    # If that happens the voltage will be low (zero) so that's how we know
    # the button was pushed.
    #
    # In that case, go through the cycle of recording a new video and playing
    # it.
    if not high_voltage_on_pin_18:
        # The first time through, we won't have any video playing, but every 
        # subsequent time, we'll already be playing the last video that we
        # recorded. We should stop playing that before we do anything else.
        print "Stopping video player (if any)."
        # Rather than mess around with killing the video player in pure Python,
        # let's cheat and just do the same thing we would do in the 
        # command-line shell.
        subprocess.call('killall omxplayer.bin', shell=True) 

        print "Preparing camera."
        # Squeeze as many frames-per-second as we can out of the little
        # PiCam. Specifically, using "mode 7" lets us go up to 90 fps.
        cam = picamera.PiCamera(framerate=90, sensor_mode=7)
        # ...but everything is a trade-off. We can't have high resolution
        # _and_ a high framerate. I'm thinking that temporal resolution is
        # more valuable here than spatial resolution. It's easy to tweak if
        # I'm wrong.
        cam.resolution = (640, 480)

        print "Recording..."
        cam.start_recording("thevid.mjpeg")
        cam.wait_recording(5)
        # We should have 5 seconds of video now, in "thevid.mjpeg".

        print "Done recording."
        cam.stop_recording()

        print "Resetting camera."
        cam.close()

        print "Playing..."
        subprocess.Popen(['omxplayer', '--no-keys', '--loop', 'thevid.mjpeg']) 
        #
        # There's some odd tricks here...
        #
        # "subprocess.Popen" let's us run the player in the background, so 
        # this program keeps running too, waiting for the next button press.
        #
        # '--no-keys' prevents the video player from expecting to have a
        # keyboard to control it, which it won't because we put it in the 
        # background (see above :D ).
        #
        # '--loop' will play the video in a loop until we say otherwise.