1559337 - nightly regression - video playback stuttery with low, highly variable framerate

Status: RESOLVED DUPLICATE of bug 1559284

(Core :: Graphics: WebRender, defect)

Description

[Steven Noonan]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0

Steps to reproduce:

This affects nightly build ID 20190613215335 but did NOT affect build ID 20190612214235.

I've tested on a fresh, empty profile with the Win64 builds from here:

Good build: https://ftp.mozilla.org/pub/firefox/nightly/2019/06/2019-06-12-21-42-35-mozilla-central/
Bad build: https://ftp.mozilla.org/pub/firefox/nightly/2019/06/2019-06-13-21-53-35-mozilla-central/

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Steps to reproduce:

• View any YouTube video. I was trying to watch this one at the time, but any should do: https://www.youtube.com/watch?v=0RxNHlqYIog

Actual results:

The video playback drops to a very low, highly variable, and stuttery framerate (though audio is fine). If I do not interact with the window or touch the mouse, the framerate occasionally drops to zero. The framerate goes up and approaches expected levels when the mouse is moving around in the Firefox window the video is being shown in.

Expected results:

The video should not have dropped below its encoded framerate.

Comment 1

[Steven Noonan]

Attachment: about:support from broken 20190613215335 build

Attaching output from about:support on the fresh profile in the broken build in case that's useful information.

Comment 2

[Steven Noonan]

As suggested in Bug 1559284 I tried disabling gfx.webrender.picture-caching and that does make the problem go away.

I'm going to mark this as duplicate.