How does VMAF decides how many threads to use

[tarun-discovery]

when we pass thread argument which lets say 32 value,
I have noticed a 20min video run with 0.9x speed, however a 3hrs video runs with 0.25x speed, what are the factors that decide this speed

[nilfm99]

@kylophone FYI, I remember a conversation a long time ago about the sublinear gains of threads.

@tarun-discovery I'd like to confirm a few things:

1. Are you passing this to the vmaf standalone executable or to ffmpeg?
2. What hardware are you running on?

[tarun-discovery]

I am passing it to ffmpeg, I am running it on k8 infra with 32vCPU

[tarun-discovery]

just to add, I tried another 3hr long video with same setup and for that video vmaf ran at 1x speed and completed in 3hrs.
So that leads me to question what are those parameters in source video that affects ffmpeg vmaf speed