usual user

OK, now that you described your network topology in more detail it is obvious what is going on.
Your router does not connect the WiFi and Ethernet segment in bridged mode but handles them as two separate segments where routing takes place and firewall rules get applied. Ports for service discovery (mdns) and LPR (printer) seem to be enabled already but for ipp-everywere or aiprint (ipp) are not.
With all properly setup and cups-browsed from the cups-filters package running there should be no user intervention be required to add the printer. cups-browsed will discover it, setup a suitable queue and in applications it will show up as printer to use.

If I looked this up correctly from the i.MX 6Solo/6DualLite Applications Processor Reference Manual the VPU has this specs:
HW Decoder: H.264 Profile: BP/CBP/MP/HP Resolution: 1080 i/p, 30 fps Bitrate: 50 Mbps
HW Encoder: H.264 Profile: BP/CBP       Resolution: 1080p, 30 fps    Bitrate: 14 Mbps
As the VPU is a dedicated IP the number of CPU cores does not matter for the codec performance and 1gb should suffice to provide the required buffer allocations for the intermediate frames.
 
Just composed my first transcode pipeline, see transcode-pipeline.pdf for reference. I do not really know what I am doing (google was my friend) and there are so much knobs for configuration and fine tuning so YMMV.
transcode-pipeline.pdf

On imx6q SoC there is:
v4l2-ctl --device=/dev/video0 --all
 v4l2-ctl --device=/dev/video1 --all
v4l2-ctl --device=/dev/video10 --all
/dev/video10 requires at least kernel 5.4.0-rc1 to work out of the box.
                  
gst-inspect-1.0 exposes:
So hardware accelerated video pipelines can be composed in all flavors.