This is the output VP9 encode which is kind of surprising considering this is using -cpu_used 4 which is basically the "fast" encoding preset of VP9. Yet it still rapes H264 as expected, about half the bitrate with only a minor hit to quality.

[Parsed_ssim_0 @ 000001dc1aad8c40] SSIM Y:0.987075 (18.885791) U:0.996881 (25.059198) V:0.995616 (23.581360) All:0.990133 (20.058130)

>An SSM score of 0.99 in video analysis typically refers to a Structural Similarity Index (SSIM) score. This score indicates a very high degree of structural similarity between two videos.
>SSIM: SSIM is a metric used to assess the perceived quality of a video by comparing it to a reference video. Unlike simple pixel-by-pixel comparisons, SSIM considers factors like luminance, contrast, and structural information, aiming to mimic how the human visual system perceives quality.
>Interpretation of 0.99: A score of 0.99 indicates that the two videos are extremely similar in terms of their structural characteristics. This is considered "very close". It suggests that the videos are likely very difficult, if not impossible, to distinguish from each other visually.

I'll encode using slower presets next but they'll probably only reduce file size by like 10% probably.