timesnap is a Node.js program that records screenshots of web pages that use JavaScript animations. It uses puppeteer to open a web page, overwrite its time-handling functions, and record snapshots at virtual times. For some web pages, this allows frames to be recorded slower than real time, while appearing smooth and consistent when recreated into a video.
You can use timesnap from the command line or as a Node.js library. It requires Node v8.9.0 or higher and npm.
To record screenshots and compile them into a video using only one command, see timecut.
# timesnap Limitations
timesnap only overwrites JavaScript functions and video playback, so pages where changes occur via other means (e.g. through transitions/animations from CSS rules) will likely not render as intended.
# From the Command Line
# Global Install and Use
To install:
Due to an issue in puppeteer with permissions, timesnap is not supported for global installation for root. You can configure npm
to install global packages for a specific user by following this guide: https://docs.npmjs.com/getting-started/fixing-npm-permissions#option-two-change-npms-default-directory
After configuring, run:
npm install -g timesnap
To use:
timesnap "url" [options]
# Local Install and Use
To install:
cd /path/to/installation/directory
npm install timesnap
To use:
node /path/to/installation/directory/node_modules/timesnap/cli.js "url" [options]
Alternatively:
To install:
cd /path/to/installation/directory
git clone https://github.com/tungs/timesnap.git
cd timesnap
npm install
To use:
node /path/to/installation/directory/timesnap/cli.js "url" [options]
# Command Line url
The url can be a web url (e.g. https://github.com
) or a file path, with relative paths resolving in the current working directory. If no url is specified, defaults to index.html
. Remember to enclose urls that contain special characters (like #
and &
) with quotes.
# Command Line Examples
# Default behavior:
timesnap
Opens index.html
in the current working directory, sets the viewport to 800x600, captures at 60 frames per second for 5 virtual seconds, and saves the frames to 001.png
to 300.png
in the current working directory. The defaults may change in the future, so for long-term scripting, it's a good idea to explicitly pass these options, like in the following example.
# Setting viewport size, frames per second, duration, and output pattern:
timesnap index.html --viewport=800,600 --fps=60 --duration=5 --output-pattern="%03d.png"
Equivalent to the current default timesnap
invocation, but with explicit options. Opens index.html
in the current working directory, sets the viewport to 800x600, captures at 60 frames per second for 5 virtual seconds, and saves the frames to 001.png
to 300.png
in the current working directory.
# Using a selector:
timesnap drawing.html -S "canvas,svg" --output-pattern="frames/%03d.png"
Opens drawing.html
in the current working directory, crops each frame to the bounding box of the first canvas or svg element, and captures frames using default settings (5 seconds @ 60fps), saving to frames/001.png
... frames/300.png
in the current working directory, making the directory frames
if needed.
# Using offsets:
timesnap "https://tungs.github.io/truchet-tiles-original/#autoplay=true&switchStyle=random" \
-S "#container" \
--left=20 --top=40 --right=6 --bottom=30 \
--duration=20 --output-directory=frames
Opens https://tungs.github.io/truchet-tiles-original/#autoplay=true&switchStyle=random (note the quotes in the url are necessary because of the #
and &
). Crops each frame to the #container
element, with an additional crop of 20px, 40px, 6px, and 30px for the left, top, right, and bottom, respectively. Captures frames for 20 virtual seconds at 60fps to frames/0001.png
... frames/1200.png
in the current working directory, making the directory frames
if needed.
# Piping:
timesnap https://breathejs.org/examples/Drawing-US-Counties.html \
-V 1920,1080 -S "#draw-canvas" --fps=60 --duration=10 \
--round-to-even-width --round-to-even-height \
--output-stdout | ffmpeg -framerate 60 -i pipe:0 -y -pix_fmt yuv420p video.mp4
Opens https://breathejs.org/examples/Drawing-US-Counties.html, sets the viewport size to 1920x1080, crops each frame to the bounding box of #draw-canvas
, records at 60 frames per second for ten virtual seconds, and pipes the output to ffmpeg
, which reads in the data from stdin, encodes the frames using pixel format yuv420p
, and saves the result as video.mp4
in the current working directory. It does not save individual frames to disk. It uses the --round-to-even-width
and --round-to-even-height
options to ensure the dimensions of the frames are even numbers, which ffmpeg requires for certain encodings.
# Command Line options
- # Output Directory:
-o
,--output-directory
directory- Saves images to a directory (default
./
).
- Saves images to a directory (default
- # Output Pattern:
-O
,--output-pattern
pattern- Sets each file name according to a printf-style pattern (e.g.
image-%03d.png
).
- Sets each file name according to a printf-style pattern (e.g.
- # Frame Rate:
-R
,--fps
frame rate- Frame rate (in frames per virtual second) of capture (default:
60
).
- Frame rate (in frames per virtual second) of capture (default:
- # Duration:
-d
,--duration
seconds- Duration of capture, in seconds (default:
5
).
- Duration of capture, in seconds (default:
- # Frames:
--frames
count- Number of frames to capture.
- # Selector:
-S
,--selector
"selector"- Crops each frame to the bounding box of the first item found by the CSS selector.
- # Viewport:
-V
,--viewport
dimensions- Viewport dimensions, in pixels. For example,
800
(for width) or800,600
(for width and height).
- Viewport dimensions, in pixels. For example,
- # Canvas Capture Mode:
--canvas-capture-mode
[format]- Experimental. Captures images from canvas data instead of screenshots. See canvas capture mode. Can provide an optional image format (e.g.
png
), otherwise it uses the saved image's extension, or defaults topng
if the format is not specified or supported. Can prefix the format withimmediate:
(e.g.immediate:png
) to immediately capture pixel data after rendering, which is sometimes needed for some WebGL renderers. Specify the canvas using the--selector
option, otherwise it defaults to the first canvas in the document.
- Experimental. Captures images from canvas data instead of screenshots. See canvas capture mode. Can provide an optional image format (e.g.
- # Start:
-s
,--start
n seconds- Runs code for n virtual seconds before saving any frames (default:
0
).
- Runs code for n virtual seconds before saving any frames (default:
- # X Offset:
-x
,--x-offset
pixels- X offset of capture, in pixels (default:
0
).
- X offset of capture, in pixels (default:
- # Y Offset:
-y
,--y-offset
pixels- Y offset of capture, in pixels (default:
0
).
- Y offset of capture, in pixels (default:
- # Width:
-W
,--width
pixels- Width of capture, in pixels.
- # Height:
-H
,--height
pixels- Height of capture, in pixels.
- # Round to Even Width:
--round-to-even-width
- Rounds width up to the nearest even number.
- # Round to Even Height:
--round-to-even-height
- Rounds height up to the nearest even number.
- # Transparent Background:
--transparent-background
- Allows background to be transparent if there is no background styling.
- # Left:
-l
,--left
pixels- Left edge of capture, in pixels. Equivalent to
--x-offset
.
- Left edge of capture, in pixels. Equivalent to
- # Right:
-r
,--right
pixels- Right edge of capture, in pixels. Ignored if
width
is specified.
- Right edge of capture, in pixels. Ignored if
- # Top:
-t
,--top
pixels- Top edge of capture, in pixels. Equivalent to
--y-offset
.
- Top edge of capture, in pixels. Equivalent to
- # Bottom:
-b
,--bottom
pixels- Bottom edge of capture, in pixels. Ignored if
height
is specified.
- Bottom edge of capture, in pixels. Ignored if
- # Unrandomize:
-u
,--unrandomize
[seeds]- Overwrites
Math.random
with a seeded pseudorandom number generator. Can provide optional seeds as up to four comma separated integers (e.g.--unrandomize 2,3,5,7
or--unrandomize 42
). Ifseeds
israndom-seed
(i.e.--unrandomize random-seed
), a random seed will be generated, displayed (if not in quiet mode), and used. Ifseeds
is not provided, it uses the seeds10,0,20,0
.
- Overwrites
- # Executable Path:
--executable-path
path- Uses the Chromium/Chrome instance at path for puppeteer.
- # Remote URL:
--remote-url
path- URL of remote Chromium/Chrome instance to connect using puppeteer.connect().
- # Puppeteer Launch Arguments:
-L
,--launch-arguments
arguments- Arguments to pass to Puppeteer/Chromium, enclosed in quotes. Example:
--launch-arguments="--single-process"
. A list of arguments can be found here.
- Arguments to pass to Puppeteer/Chromium, enclosed in quotes. Example:
- # No Headless:
--no-headless
- Runs Chromium/Chrome in windowed mode.
- # Screenshot Type:
--screenshot-type
type- Output image format for the screenshots. By default, the file extension is used to infer type, and failing that,
png
is used.jpeg
is also available.
- Output image format for the screenshots. By default, the file extension is used to infer type, and failing that,
- # Screenshot Quality:
--screenshot-quality
number- Quality level between 0 to 1 for lossy screenshots. Defaults to 0.92 when in canvas capture mode and 0.8 otherwise.
- # Start Delay:
--start-delay
n seconds- Waits n real seconds after loading the page before starting the virtual timeline.
- # Quiet:
-q
,--quiet
- Suppresses console logging.
- # Output stdout:
--output-stdout
- Outputs images to stdout. Useful for piping.
- # Version:
-v
,--version
- Displays version information. Immediately exits.
- # Help:
-h
,--help
- Displays command line options. Immediately exits.
# From Node.js
timesnap can also be included as a library inside Node.js programs.
# Node Install
npm install timesnap --save
# Node Examples
# Basic Use:
const timesnap = require('timesnap');
timesnap({
url: 'https://tungs.github.io/truchet-tiles-original/#autoplay=true&switchStyle=random',
viewport: {
width: 800, // sets the viewport (window size) to 800x600
height: 600
},
selector: '#container', // crops each frame to the bounding box of '#container'
left: 20, top: 40, // further crops the left by 20px, and the top by 40px
right: 6, bottom: 30, // and the right by 6px, and the bottom by 30px
fps: 30, // saves 30 frames for each virtual second
duration: 20, // for 20 virtual seconds
outputDirectory: 'frames' // to frames/001.png... frames/600.png
// of the current working directory
}).then(function () {
console.log('Done!');
});
# Multiple pages:
const timesnap = require('timesnap');
var pages = [
{
url: 'https://tungs.github.io/truchet-tiles-original/#autoplay=true',
outputDirectory: 'truchet-tiles'
}, {
url: 'https://breathejs.org/examples/Drawing-US-Counties.html',
outputDirectory: 'counties'
}
];
(async () => {
for (let page of pages) {
await timesnap({
url: page.url,
outputDirectory: page.outputDirectory,
viewport: {
width: 800,
height: 600
},
duration: 20
});
}
})();
# Node API
The Node API is structured similarly to the command line options, but there are a few options for the Node API that are not accessible through the command line interface: config.logToStdErr
, config.frameProcessor
, config.preparePage
, config.preparePageForScreenshot
, and certain config.viewport
properties.
timesnap(config)
- #
config
<Object>- #
url
<string> The url to load. It can be a web url, likehttps://github.com
or a file path, with relative paths resolving in the current working directory (default:index.html
). - #
outputDirectory
<string> Saves images to a directory. Makes one if necessary. - #
outputPattern
<string> Sets each file name according to a printf-style pattern (e.g.image-%03d.png
) - #
fps
<number> Frame rate, in frames per virtual second, of capture (default:60
). - #
duration
<number> Duration of capture, in seconds (default:5
). - #
frames
<number> Number of frames to capture. Overrides default fps or default duration. - #
selector
<string> Crops each frame to the bounding box of the first item found by the specified CSS selector. - #
viewport
<Object>- #
width
<number> Width of viewport, in pixels (default:800
). - #
height
<number> Height of viewport, in pixels (default:600
). - #
deviceScaleFactor
<number> Device scale factor (default:1
). - #
isMobile
<boolean> Specifies whether themeta viewport
tag should be used (default:false
). - #
hasTouch
<boolean> Specifies whether the viewport supports touch (default:false
). - #
isLandscape
<boolean> Specifies whether the viewport is in landscape mode (default:false
).
- #
- #
canvasCaptureMode
<boolean | string>- Experimental. Captures images from canvas data instead of screenshots. See canvas capture mode. Can provide an optional image format (e.g.
png
), otherwise it uses the saved image's extension, or defaults topng
if the format is not specified or supported. Can prefix the format withimmediate:
(e.g.immediate:png
) to immediately capture pixel data after rendering, which is sometimes needed for some WebGL renderers. Specify the canvas by settingconfig.selector
, otherwise it defaults to the first canvas in the document.
- Experimental. Captures images from canvas data instead of screenshots. See canvas capture mode. Can provide an optional image format (e.g.
- #
start
<number> Runs code forconfig.start
virtual seconds before saving any frames (default:0
). - #
xOffset
<number> X offset of capture, in pixels (default:0
). - #
yOffset
<number> Y offset of capture, in pixels (default:0
). - #
width
<number> Width of capture, in pixels. - #
height
<number> Height of capture, in pixels. - #
transparentBackground
<boolean> Allows background to be transparent if there is no background styling. - #
roundToEvenWidth
<boolean> Rounds capture width up to the nearest even number. - #
roundToEvenHeight
<boolean> Rounds capture height up to the nearest even number. - #
left
<number> Left edge of capture, in pixels. Equivalent toconfig.xOffset
. - #
right
<number> Right edge of capture, in pixels. Ignored ifconfig.width
is specified. - #
top
<number> Top edge of capture, in pixels. Equivalent toconfig.yOffset
. - #
bottom
<number> Bottom edge of capture, in pixels. Ignored ifconfig.height
is specified. - #
unrandomize
<boolean | string | number | Array<number>> OverwritesMath.random
with a seeded pseudorandom number generator. If it is a number, an array of up to four numbers, or a string of up to four comma separated numbers, then those values are used as the initial seeds. If it is true, then the default seed is used. If it is the string 'random-seed', a random seed will be generated, displayed (if quiet mode is not enabled), and used. - #
executablePath
<string> Uses the Chromium/Chrome instance atconfig.executablePath
for puppeteer. - #
remoteUrl
<string> URL of remote Chromium/Chrome instance to connect usingpuppeteer.connect()
. - #
launchArguments
<Array <string>> Extra arguments for Puppeteer/Chromium. Example:['--single-process']
. A list of arguments can be found here. - #
headless
<boolean> Runs puppeteer in headless (nonwindowed) mode (default:true
). - #
screenshotType
<string> Output image format for the screenshots. By default, the file extension is used to infer type, and failing that,'png'
is used.'jpeg'
is also available. - #
screenshotQuality
<number> Quality level between 0 to 1 for lossy screenshots. Defaults to 0.92 when in canvas capture mode and 0.8 otherwise. - #
startDelay
<number> Waitsconfig.startDelay
real seconds after loading before starting (default:0
). - #
quiet
<boolean> Suppresses console logging. - #
logToStdErr
<boolean> Logs to stderr instead of stdout. Doesn't do anything ifconfig.quiet
is set to true. - #
frameProcessor
<function(Buffer, number, number)> A function that will be called after capturing each frame. Ifconfig.outputDirectory
andconfig.outputPattern
aren't specified, enabling this suppresses automatic file output. After capturing each frame,config.frameProcessor
is called with three arguments, and if it returns a promise, capture will be paused until the promise resolves: - #
preparePage
<function(Page)> A setup function that will be called one time before taking screenshots. If it returns a promise, capture will be paused until the promise resolves.page
<Page> The puppeteer instance of the page being captured.
- #
preparePageForScreenshot
<function(Page, number, number)> A setup function that will be called before each screenshot. If it returns a promise, capture will be paused until the promise resolves.
- #
- # returns: <Promise> resolves after all the frames have been captured.
# timesnap Modes
timesnap can capture frames using one of two modes:
- # Screenshot capture mode (default) uses puppeteer's built-in API to take screenshots of Chromium/Chrome windows. It can capture most parts of a webpage (e.g. div, svg, canvas) as they are rendered on the webpage. It can crop images, round to even widths/heights, but it usually runs slower than canvas capture mode.
- # Canvas capture mode (experimental) directly copies data from a canvas element and is often faster than using screenshot capture mode. If the background of the canvas is transparent, it may show up as transparent or black depending on the captured image format. Configuration options that adjust the crop and round to an even width/height do not currently have an effect. To use this mode, use the
--canvas-capture-mode
option from the command line or setconfig.canvasCaptureMode
from Node.js. Also specify the canvas using a css selector, using the--selector
option from the command line or settingconfig.selector
from Node.js, otherwise it uses the first canvas element.
# How it works
timesnap uses puppeteer's page.evaluateOnNewDocument
feature to automatically overwrite a page's native time-handling JavaScript functions and objects (new Date()
, Date.now
, performance.now
, requestAnimationFrame
, setTimeout
, setInterval
, cancelAnimationFrame
, cancelTimeout
, and cancelInterval
) to custom ones that use a virtual timeline, allowing for JavaScript computation to complete before taking a screenshot.
This work was inspired by a talk by Noah Veltman, who described altering a document's Date.now
and performance.now
functions to refer to a virtual time and using puppeteer
to change that virtual time and take snapshots.