1872710 - Youtube is lagging significantly to the point where it is unwatchable a 2x speed on Macbook Air

Status: UNCONFIRMED

(Core :: Audio/Video: Playback, defect, P3)

Description

[hansowen.m]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:121.0) Gecko/20100101 Firefox/121.0

Steps to reproduce:

Use Intel based Macbook Air 2019 Core i5 1.6GHz Dual Core.
Ensure highspeed internet connection 300Mbps+.
Open firefox.
Open youtube.
Pick a 1080p 60fps video.
Speed up 2x.

Actual results:

Video lags and is unwatchable. However audio is fine.

Expected results:

Video plays smoothly at 2x speed at 1080p 60fps withput stuttering or lagging.

Comment 1

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Core::Audio/Video: Playback' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Mayank Bansal]

Can you:

1. Open about:support in your browser and paste its contents to this bug
2. Capture a Firefox performance profile as outlined here : https://profiler.firefox.com/docs/#/ . Please select the "Media" prest before capturing the profile.
3. If this is a recent issue and Firefox worked good for you previously, please do a bisection using this tool https://mozilla.github.io/mozregression/ . That will pinpoint the exact regression.

Comment 3

[hansowen.m]

Attachment: about:support raw data

about:support

Comment 4

[hansowen.m]

Firefox Profile
https://share.firefox.dev/41GQaYo

Comment 5

[Jim Mathies [:jimm]]

Looks like we're spending most of the time in display list code. Might be expected, Macbook Air 2019 playing back 1080p at 2x speed. Marcus, do see anything in this profile that sticks out? There's also an add-blocker extension running but I don't see anything related to that in the profile.

Comment 6

[Alastor Wu [:alwu]]

Attachment: profiler_slow_video_decoding.png

Hello, does this issue only happen on when you watching 60fps video in 2x speed? Does it happen on lower playback rate, eg. 1.5x? or does it happen for 30fps video as well?

By checking the profiled result in comment4, I saw some video frames was dropped because video decoding was too late. For 60fps, each video frames is around 16ms. There were some frames, specially keyframes took way longer time to decode.

Does this issue also happen on other browsers? If so, that might indicate that the hardware is not strong enough for 60fps. If not, then we can do other further investigation.

Thank you.

Comment 7

[hansowen.m]

This issue only happens when watching 60fps video in 2x speed on YouTube (however have not tested other streaming platforms). When switching to a lower playback rate, e.g., 1.5x, playback is normal. I tested other browsers alongside firefox to check if it was an issue with my Mac hardware, however, both Safari and Chrome were able to reliably playback 1080p 60fps video at 2x speed on Youtube without any lag/dropped frames. Therefore, I believed the issue may be associated with firefox and I submitted this bug report.

Comment 8

[Markus Stange [:mstange]]

(dropping needinfo since :alwu is taking a look)

Comment 9

[Alastor Wu [:alwu]]

Thanks! Add NI to myself for checking this again.