Tested on the OSX 10.11.4 with Nightly 58.0a1 (2017-10-25). This 4K vp9 video [1] would drop lots of frames during playing, and the video would be jittering. But won't see the issue when playing other 4K vp9 video [2] [1] https://www.youtube.com/watch?v=R3AKlscrjmQ [2] https://www.youtube.com/watch?v=KvNis_A6UaI&t=10m45s https://www.youtube.com/watch?v=0wCC3aLXdOw https://www.youtube.com/watch?v=Bey4XXJAqS8

It looks ok on my local with nerd stats on, FF 58.0a1 (2017-10-25) nightly on mac 10.12.6.

From stats for nerds, it looks [1] is 60fps and [2] is 30 fps. From another angle, comparing it with Chrome would be more meaningful.

(In reply to Alfredo Yang (:alfredo) from comment #1) > It looks ok on my local with nerd stats on, FF 58.0a1 (2017-10-25) nightly > on mac 10.12.6. Please ignore my comment, a misunderstanding.

Note, you may need to change resolution manually to 4K and make sure it's 60fps and with vp9 codec.

It really depends on computer's capabilities, so a better way to check if frames dropped is normal or not is to compare the number of that between Firefox and Chrome/Edge/Safari. Can you do some comparisons and provide some numbers?

(In reply to Blake Wu [:bwu][:blakewu] from comment #5) > It really depends on computer's capabilities, so a better way to check if > frames dropped is normal or not is to compare the number of that between > Firefox and Chrome/Edge/Safari. > Can you do some comparisons and provide some numbers? On those particular video, on Linux, my xps 15 will drop frames, but not in Chrome, and not if e10s is disabled.

The dropped frame number when playing 20s video is * Chrome 36/1234 , Firefox 957/1233 Tested on my laptop, MacBook Pro (Retina, 15-inch, Mid 2014).

I'm marking this as P3 on the basis that VP9 is disabled for MSE on Mac OSX.

I can see this problem on my windows laptop as well, so this is not a Mac specific bug. Given that, we should set this bug as P2.

(In reply to Blake Wu [:bwu][:blakewu] from comment #9) > I can see this problem on my windows laptop as well, so this is not a Mac > specific bug. > Given that, we should set this bug as P2. your machine has VP9 HW acceleration it may not be the same problem... It's also certainly unrelated to bug 1414596 has this is due to a compilation issue of the ffvp9 decoder which went in after this bug was opened. However, it's possible that the measurement of comment 7 are due to the ffvp9 problem following the resync

Now that bug 1414596 is in, could you retest thank you.

I reproduced this issue with "media.mediasource.webm.enabled=true", so it's not related with benchmark. Since the same video could be playback more smoothly on Chrome, I believe my computer has ability to play vp9. I re-test the video again, this time I play video after it's well-buffered, because the buffering seems affecting the dropped frame on Chrome. I record the dropped frame data three times. [video] https://www.youtube.com/watch?v=R3AKlscrjmQ [dropped frame] (1) : Chrome 11/752, Firefox 415/621 (2) : Chrome 6/942, Firefox 410/591 (3) : Chrome 4/706, Firefox 386/620

Chrome doesn't measure frame drops really as it pauses instead of dropping frames in most cases. But you're likely hitting the issue on why vp9 was disabled on Mac in the first place. Bug 1403412