How to make screenshots on chromecast? - chromecast

Question

I would like to make screenshots of the receiver application running of the Chromecast device.
I need to have it running on the device to show the video and the application together.
Is there a way to do this ?

Answer 1

Ali Naddaf's answer is technically true, however with a little work I was able to make a faithful reconstruction of the screen, to the point that it is indistinguishable from an actual screenshot.
We will use code from the html2canvas project, see http://html2canvas.hertzen.com/documentation.html . It will render our screen to a canvas. In particular, copy&paste the compiled code from http://html2canvas.hertzen.com/build/html2canvas.js to the Chromecast console. (adding a tag to dom seems not to work) You can access the Chromecast console & developer tools by accessing the ip.ad.dr.ss:9222 port via Chrome.
Issue the following command:
html2canvas(document.body, {onrendered: function(canvas){document.write('');}});
This will destructively replace the screen with the screenshot (I find this convenient but you can easily think of a more polite way if you wish)
In the elements browser, you will have an img, with a base64 url specified as a src. Click on the url, chrome will open the image in a new tab. Hopefully it's the screenshot that you wanted.
You might find that some pictures are missing because of e.g. same origin policy. The javascript have other privileges than accessing images from html. If this happens, work it out somehow (use https for images for example), then goto 1.
You have your screenshot!

Answer 2

No, that is not possible due to many reasons such as media rights and security.

Answer 3

I'm extending zsolt-szatmari's answer into a copy-pastable script that you can use in the Chromecast Developer Tools console:
As he said, copy and paste http://html2canvas.hertzen.com/build/html2canvas.js code into the console
Call the html2canvas method: it will create a new canvas element into the DOM: html2canvas(document.body, { onrendered: function(canvas) { document.body.appendChild(canvas); } });.
Get a base64 string representation of the image currently displayed in the canvas: document.getElementsByTagName('canvas')[0].toDataURL('image/png');
You'll then get a very long base64 string: if you click on it, Chrome will show the image in a new tab. Please note that this image could be far from what is really shown on your Chromecast due to html2canvas limits:
The screenshot is based on the DOM and as such may not be 100%
accurate to the real representation as it does not make an actual
screenshot, but builds the screenshot based on the information
available on the page.
(source)

Answer 4

I was thinking that you could maybe use this to capture the canvas to an image file, which normally works in javascript with canvas:
var canvas = document.getElementById("mycanvas");
var img = canvas.toDataURL("image/png");
Of course then you would need to transfer this image file to somewhere - not exactly sure how to the last bit from the chromecast. Maybe that is not possible.
As a chromecast developer myself I needed screenshots of the app running to show customers. I ended up doing a kind of "simulation" of the chromecast - calling some mockup methods in javascript to display the data and then accessing my receiver app via the cast url on my desktop in the browser. Then I used a screen capture program to capture the browser output. This gave me the same screenshot as from running the receiver app on chromecast on TV, which is essentially just a browser showing your html+css+javascript receiver.