startScreencast feature?

Would be great to screencast the page.

[Garbee]

Why screencast a headless display? If you want to see it, simply don't start it in headless mode.

Good point. In other words if there is a need to screencast page - one have to use Chromium without headless mode.

On the other hand puppeteer supports non-headless mode too. Would be great that Puppetier would support this: https://chromedevtools.github.io/devtools-protocol/tot/Page/#method-startScreencast

[nigeon]

+1

[aslushnikov]

@Mykolas-Molis how do you want to consume it? Do you want to save a screencast as a video file?

[michaelshiel]

I've implemented this for myself over here: https://github.com/michaelshiel/puppeteer (Page emits an event for each frame) but I'm not sure what kind of tests would be appropriate, or how to describe/structure them, any suggestions?

[sul4bh]

@aslushnikov I would like to have this feature implemented too. My use case is recording the screen as a video.

[paulirish]

+1 to video capture start/stop/save API

[sul4bh]

Not sure where to ask this question but here it goes:
What does the document here(https://chromedevtools.github.io/devtools-protocol/tot/Page/#method-startScreencast) mean by a frame? What is the maximum frame-rate that I might be able to get by using startScreencast()?

I experimented with startScreencast() but I was only able to get about 5fps (meaning 5 png images/frames in 1 second). On headless mode I got only 1 fps. This is a very low fps for video.

[michaelshiel]

I think it depends on how much the page is changing, in my experience it will stop sending frames if there are no changes on the page. I tried it on a youtube video, and I was getting at least 20 frames per second.

[sul4bh]

@michaelshiel you are right. I played a 25fps youtube video and got an average of 25 "frames" per second. EDIT: Can't verify if the frames are generated only when the content of the screen changes. EDIT: Verified

Also I got really high fps today. Not sure why it was low yesterday. Probably Chrome Canary got updated or something...

Also, it would be nice to have a Viewport option for startScreencast(). (not sure where to request for a feature)

[KeizerDev]

Check this issue: ChromeDevTools/devtools-protocol#17