force transcode to av1

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I don't think so in the current version.  

Also from the last tests i've seen (about 6 months ago) with hardware encoding Nvidia was practically the same quality with their H265/AV1 (Quality Profile 10Bit) encoding using Nvidia 4000 series.
On Intel (Quality Profile 10Bit) H265 actually offered better quality for the same bitrate over their AV1 Encoding in the Arc series cards.  So at least with this generation of GPUs i don't think AV1 transcoding is worthwhile.

Of course software encoding will give better results, but the CPU requirements are off the charts.

I mean quality isn't the metric that AV1 is made to compete on. It's quality for bitrate and AV1 wins almost every time, save for a few niche cases. Additionally, AV1 being an open codec is a huge plus over HEVC. There are flaws, and while I was just getting my x265 encodes pretty flawless (and fast with QSV), I've jumped ship to AV1 instantly looking at the quality, size, and knowing it's an open standard. Even though it's slow, with interesting tools like ab-av1, you get what you're looking for 100% of the time.