Seems legit per chat conversations with Caleb. Dan, Chris do you see anything on canary locally?

(Don't have a mac with me or would test myself).

This repros on stable (55.0.2883.95) as well. 

We recently upgraded the two macs in the lab to Sierra, so that could be the problem. 

I think that this is a result of a problem with the linux recorder rather than a problem with all playbacks. This should not repro unless you have an external display connected over HDMI. Even then, I'm worried that this is caused by some misconfiguration with the recorder somehow such that you might not see it if you connect it up to other HDMI outputs (such as an external monitor)

Note that I observed this on the internal display of the mac, but only when they were outputting to HDMI. 

I will research further. No need for alarm yet.

This problem started happening after we upgraded those machines to Sierra. Vitali reimaged the macbook_pro to el capitan, and the problem disappeared.

Pretty sure this regression was caused by the upgrade to Sierra. However, I'm having a lot of trouble getting it to repro manually.

Now the problem seems to be worse. It is happening on both 

Safari: https://av-analysis.corp.google.com/#/get-testpass-details/2/Video%20Stack/235938

and

Chrome: https://av-analysis.corp.google.com/#/get-testpass-details/2/Video%20Stack/235936

For both of them, the video plays poorly for a couple seconds and then freezes completely.

These bugs cause dropped frames, but only in automation. I can repro it manually. It isn't caused by the HDMI because I unplugged the HDMI and used webkitDroppedFrameCount value. The value was still abnormally high even with the HDMI unplugged (it was a little bit better IIRC).

I'm lowering this to P2 since it seems like a webdriver/automation issue. I will have to get to it in Q1.

Comment 6:
s/can repro it manually/can't repro it manually/

I don't see this issue repro anymore on macbookpro-i5-5257u-inteliris6100 device run on 2/3~2/10.

re-activate this bug and give to caleb. the bug is not seen on macbookpro because that machine is downgraded to not use OSX sierra

I don't know how to fix this. Marking available. If anyone wants to take this on (with my help) then feel free.

Setting next action to March 26th to see if we can put it in planning for next quarter.

The NextAction date has arrived: 2018-03-26

The NextAction date has arrived: 2018-04-02

Assigning to myself to do another investigation. Priority increased to P1 since Safari seems to have improved.

This seems you have been fixed somehow :D

https://av-analysis.corp.google.com/#get-testpass-details/2/Video%20Stack/713074

Vitali, can you please check that macbook_corem_5y31_intelhd5300 is running Sierra or newer?

It's running MacOs Sierra 10.12.6

This issue has been resolved on its own. It's unclear whether the fix came from a Chrome update or a MacOS update, but it is fixed.