none, you aren't using gpu, just whatever cpu is the fastest. if you want gpu acceleration you have to specify it. and keep note gpu acceleration is less efficient then cpu so your files will be bigger. though at preset fast it might actually be pretty close
Yes this is indeed what I said. but well calling gpu encoders "worse" isnt really fair, it's all trade offs, they for sure have worse efficiency as we both said, but their speed is significantly faster usually. I would say that doesn't make the encoder "worse" just different.
You may want to ask over in !datahoarder@lemmy.ml . This topic often came up back on Reddit, and the general vibe I got was that most people prefer QuickSync. Intel may not be great in a lot of areas, but they are a beast in video encoding/decoding. That being said, I use a Ryzen APU and it's perfectly fine. There are way more important things to look at when choosing a CPU.
If your performance is slow, I would check your CPU is listed on the chart I linked above. Not all CPUs support all codecs.
Edit: If your CPU doesn't support the codec, it will still work, it just won't be accelerated.
quicksync really doesn't have good quality:compression buying a used nvidia gpu and using that would be far better. but really, any moderatly up to date cpu should get good x265 or svtav1 perf
As far as I know and could look up on short notice, libx265 does not make use of GPU computing (via CUDA or otherwise), so the answer to your second question
Would tight integration between amd cpu + gpu help in this case?
is almost certainly no.
Performance wise, the ffmpeg command you posted will be completely dominated by the video encoding part through libx265, to the point where everything else is pretty much negligable. Also, the rest of this does not use gpgpu computing either.