Open Bug 1604671 Opened 1 year ago Updated 4 days ago

getDisplayMedia limiting framerate


(Core :: WebRTC: Audio/Video, defect, P2)

71 Branch



Tracking Status
firefox71 --- affected
firefox72 --- affected
firefox73 --- affected


(Reporter: michael.whittemore, Unassigned)


(Blocks 1 open bug)



(1 file)

Attached file captureScreen.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.79 Safari/537.36

Steps to reproduce:

  1. Open the included file, this will share your screen
  2. Move your mouse around, quickly
  3. Notice the latency

Given that the fps was set at a high rate, 30 fps, there shouldn't be any noticeable delay.

Actual results:

There is some noticeably delay. The mouse movement displayed was sluggish, much slower than the configured rate of 30 fps.

Expected results:

There should be no (noticeable) delay when sharing the screen since the fps was configured at a high rate. For contrast, this worked fine in Chrome and Safari.

I was able to reproduce it on latest Nightly version 73.0a1 Build ID 20191222215627, Beta Version 72.0b10 Build ID 20191221003008 and FFF release Version 71.0 Build ID 20191202093317 on macOS 10.14.5.
I changed Product and Component. DOM Events team if this is not the right component please feel free to route this ticket to the corresponding team, thanks!

Component: Untriaged → DOM: Events
Ever confirmed: true
Product: Firefox → Core
Component: DOM: Events → WebRTC
Priority: -- → P2
Component: WebRTC → WebRTC: Audio/Video

The problem still occurs with Firefox Nightly 77.0a1 (2020-04-22).

To determine the real framerate I sent the stream through a media recorder and analyzed the resulting file: The recorded framerate is between 4-5 fps, which is significantly below what you would perceive as a halfway smooth motion.

The test case of michael.whittemore is best viewed with firefox nightly as you can now see the cursor, which makes spotting the bug visually very easy.

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