Name: lava-frame_compare
Owner: BBC
Description: null
Created: 2016-01-18 20:32:12.0
Updated: 2016-01-24 20:45:55.0
Pushed: 2016-07-13 12:25:44.0
Homepage: null
Size: 2353
Language: Ruby
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Helpers for analysing video frames and screenshots over a testing session, analyzing them, and stitching them together for later playback.
We use our lava libs for checking video playback on our device tests.
We run a lot of tests that capture screenshots or look at video playback. Often we'll take several screenshots or video samples over the duration of a test and we wanted some way of comparing the captures over the test run in order to determine if video playback is working.
Lava performs a diff between frames and returns an integer representing the amount of change between screenshots. A value of zero indicates the frames are identical. Whereas a value in the thousands indicates a large differential between the frames. We find this diff technique gives us a good indication that video is playing in our tests, and will also spot buffering problems and crashes (the diff value drops significantly).
Lava also stitches together the frames captured over a session to create an animated gif that is a handy reference for checking why a particular test failed.
The gem is very simple and doesn't do any captures itself – you'll need to have some mechanism for doing that. We use the device_api gem for grabbing screenshots from physical android and ios devices.
The gem uses ImageMagick to perform the frameshot comparisons – you will need to install this dependency first.
You first need to define a lambda for performing a capture. For example, using the device_api we might do:
take_screenshot = ->(filename) {
device.screenshot(:filename => filename)
}
You can then use that lambda with Lava to establish a capture session, giving it a directory where you want the screen shots.
session = Lava::FrameCompare.start_session( :name => 'test-01', :capture => take_screenshot, :dir => 'captures' )
# Call capture for the initial screenshot
frame = session.capture
# session.diff performs a screenshot and does the diff
10.times do
puts session.diff
end
# Finish the session and create the composite
session.end( file: './composite.gif' )
There are a number of options for generating the composit file:
# Create a significantly smaller gif file by skipping every other frame
session.end( :step => 2 )
# Speed up the gif playback
session.end( :speed => 5) # 5x speed
# Rotate the image
session.end( :rotate => 90 ) # 90 degrees
# Set the max dimensions of the image
session.end( :max_width => 100, :max_height => 100 )
Lava is available to everyone under the terms of the MIT open source licence. Take a look at the LICENSE file in the code.
Copyright (c) 2016 BBC