[Webkit-unassigned] [Bug 251017] [GStreamer] 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

--- Comment #11 from Jeff Fortin <nekohayo at gmail.com> ---
Using unrud's VideoDownloader (see https://flathub.org/apps/details/com.github.unrud.VideoDownloader ...) to download the 4K VP9 version of any 4K sample on youtube (https://www.youtube.com/watch?v=OfNJro9jGdE is the one I tested now, but probably any other would yield the same result), giving it a simpler filename and playing it like so:

GST_PLUGIN_FEATURE_RANK=vah264dec:MAX,vah265dec:MAX,vampeg2dec:MAX,vavp8dec:MAX,vavp9dec:MAX gst-play-1.0 --videosink glimagesink 4k_hdr_sample.webm

or, more succintly:

GST_PLUGIN_FEATURE_RANK=vavp9dec:MAX gst-play-1.0 --videosink glimagesink 4k_hdr_sample.webm

...results in 100% smooth video playback on this Intel Kabylake laptop with 4K screen, where intel_gpu_top shows the video decoder is correctly used.

If I don't prefix it with the GST_PLUGIN_FEATURE_RANK env var, then it doesn't use the hardware decoder at all (as indicated by intel_gpu_top) and is unplayable, it can't keep up at all.

If I don't use `--videosink glimagesink`, then it does use the hardware decoder but playback is not butter-smooth (it can keep up, though).

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