Not a USB/PiHat answer, but the NEC "EMMA" chipset used in Topfield/Humax? PVRs have a "filter" where you can specify which streams you want the hardware to decode and push across. Normally, it would be programmed to supply the data/video/audio streams for the channel you are interested in, which are buffered and shovelled to disk -- but there was a "proof of concept" TAP for Topfield PVRs that reprogrammed the filter, so that the filters were opened wide, to allow recording the WHOLE mux to disk at once.
It required some equivalent interference in the playback of the .REC file which contained multiple video/audio streams -- now suddenly the filters need to be loaded to screen out the unwanted data coming from disk, on playback!
As the Topfield is twin-tuner, that meant in theory, recording two entire muxes to disk was possible at a hardware level, without overtaxing the CPU at all.
So it does seem to be a hardware feature, going back some years, to at least attempt to throttle the amount of data being flung around.