[Webkit-unassigned] [Bug 251017] New: [GTK] VA-API (GstVA) hardware-accelerated video decoding playback above 1080p resolution on YouTube in VP9 is very slow and stutters

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=251017

            Bug ID: 251017
           Summary: [GTK] VA-API (GstVA) hardware-accelerated video
                    decoding playback above 1080p resolution on YouTube in
                    VP9 is very slow and stutters
           Product: WebKit
           Version: Other
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKitGTK
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: nekohayo at gmail.com
                CC: bugs-noreply at webkitgtk.org

Test case: playing https://www.youtube.com/watch?v=mBw7vkcQOew in 1080p and above resolutions ("stats for nerds" reveals it is playing using the VP9 codec on my computer)

Here are the specs and parameters of my main testing computer (but it was observed on various other people's computers as well, particularly on HiDPI screens):

* HP Spectre X360 laptop (15" 2018 model) with 4K HiDPI display, featuring an 8th generation (Kabylake) Intel Core i7 CPU and the associated intel graphics chipset, 16 GB of RAM and NVMe SSD
* Running on the Wayland GNOME session on Fedora 37, with GNOME's night light & dark mode turned off (just to make sure this can't interfere)
* Testing with the "technology preview" Epiphany Devel flatpak package from the gnome-nightly repository for consistency/simplicity

---

## Setup and reproduction instructions

* On Fedora, it might be that the gstva plugin is part of this package (I'm not sure), so I did: `dnf install gstreamer1-plugins-bad-*-extras`. Make sure to also have `libva libva-utils libva-intel-driver` and `igt-gpu-tools` (to have the `intel_gpu_top` commandline utility available)
* Grab Epiphany.Devel from gnome-nightly as a flatpak, and then run it like this (loosely based on https://blogs.igalia.com/vjaquez/2021/12/08/gstva-in-gstreamer-1-20/ ):

`flatpak run --env=GST_PLUGIN_FEATURE_RANK=vah264dec:MAX,vah265dec:MAX,vampeg2dec:MAX,vavp8dec:MAX,vavp9dec:MAX org.gnome.Epiphany.Devel`

...then try to play https://www.youtube.com/watch?v=mBw7vkcQOew at a resolution higher than 1080p.

## Results

Regardless of dark/light mode (better to test in light mode to avoid conflating with bug #251016), attempting to play https://www.youtube.com/watch?v=mBw7vkcQOew in VP9 with VA-API through GstVa (for hardware that supports it, such as Intel Kabylake) at any resolution higher than 1080p will lag like hell, whether in HiDPI or not (but I could expect that the problem would probably be worse on a HiDPI screen, if previous bug reports are any indication).

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