Confusion about "Video Engine Utilization"

[akorb]

First, thanks for your amazing work, I appreciate that you spend your time on this.

Now, I installed libva-nvidia-driver on my Manjaro system and enabled VA-API (media.ffmpeg.vaapi.enabled). That's all I did. I'm on driver 550.78, X11, and an NVIDIA GeForce RTX 4070 SUPER.

Thereby, I receive this result in about:support, which is great:

However, the GPU Utilization and Video Engine Utilization metrics in the NVIDIA settings behave differently depending on whether I set MOZ_DISABLE_RDD_SANDBOX=1.

For the following values, I used the YouTube video Norway 4K as reference (2160p, AV1).

MOZ_DISABLE_RDD_SANDBOX=0 firefox

Keeping the RDD sandbox enabled results in reoccuring console outputs like this

libva error: /usr/lib/dri/nvidia_drv_video.so init failed

GPU Utilization: 10 - 25% Video Engine Utilization: 0%

MOZ_DISABLE_RDD_SANDBOX=1 firefox

No console output. GPU Utilization: ~2% Video Engine Utilization: 5-10%

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What confuses me is that firefox claims either way that HW Decoding support is enabled, and that the GPU is always somehow used (either as GPU or Video Engine) when streaming a video.

My first wild theory is that with the RDD sandbox enabled the VA-API driver uses the direct backend, which consequently uses CUDA, which is not represented in Video Engine Utilization but GPU Utilization.

My second theory is that the table HW support table in about:support as attached at the top is unreliable. Maybe firefox detects a VA-API driver and therefore thinks HW decoding is available, even though this VA-API driver cannot actually launch the hardware decoding because the sandbox is still enabled.

I'm asking because overall, if possible, I'd prefer to leave the RDD sandbox enabled, since it has security benefits. And if both options are valid MOZ_DISABLE_RDD_SANDBOX=*, I'd not disable the sandbox.

[brokeDude2901]

I'm using nvidia-driver-555 from ubuntu-graphics-drivers ppa and Video Decoding Engine just disappears:

[akorb]

I think it's really that firefox shows the table wrong. When I enable the logs (NVD_LOG=1), it shows with the RDD sandbox enabled:

init ERROR: Potential Firefox sandbox detected, failing to init!
init If running in Firefox, set env var MOZ_DISABLE_RDD_SANDBOX=1 to disable sandbox.