[Reg 6.5.6 -> 6.5.7 and 6.6.3 -> 6.7.0] WebEngineView: Bad performance with jitsi when using background blur/image

Qt User reported that when they use Qt WebEngine with Jitsi meeting services with blurred background the video feed goes very slow:
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We use WebEngineView to embed Jitsi video conferencing in our application.

Starting with Qt 6.7 (I think this release brought some important RHI changes required to get Chromium GPU rendering) this now generally works fine on Windows with the 3d11 rhi backend.

However we have received reports from users complaining about bad performance when the JITSI background options (image or blur) are being activated.

When using e.g. Chrome instead, this is not an issue.

I was able to reproduce the problem and to localize the bottleneck to be a canvas.drawImage call, with the HTML video element used as source + another canvas containing the segmentationMask (used to mask the silhouette) for composition.
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Reproducer example attached:

Start the example.
Press "Start meeting"
Press "Select background" 4th additional option under Join meeting.
Select Blur and ok.
Video feed becomes very slow.