FFmpeg: What are the h264_vaapi and hevc_vaapi encoders? How do they work? Do they just use the Video Coding Engine / Encoding ASIC on AMD GPUs?

The last part especially is what I'm wondering. How exactly does VAAPI work? Does it just use the the way that NVENC or h264_amf and hevc_amf works? Would it be possible to use the main GPU cores on either Nvidia or AMD cards?

From what I found from looking up the h264_vaapi and hevc_vaapi encoders, they're just the linux equivalents of h264_amf and hevc_amf, right?

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