I'm trying to download multiple streams at once and notice that when my CPU hits 100 percent usage I start to lose bitrate in the streams slightly.

Is it possible to offload some of these to the graphics card for processing? NVENC would be a good one for me.

I imagine its something that I have to find in a build or build from source to achieve.

Has anyone done this and was it worthwhile?

I will assume you are referring to live streams since no re-encoding is performed for on-demand programmes. If you have a version of ffmpeg built with NVENC support it might be possible. You would use --hls-livetv-opts to feed the necessary options to ffmpeg when it is launched by get_iplayer. I have no idea if it would actually work. You should be able to switch off the re-encoding in 2.94 with --hls-livetv-opts="-c:a copy -c:v copy". However, you would also need an updated version of ffmpeg (> 2.5) configured via --ffmpeg. The development version of get_iplayer turns the re-encoding off by default for live TV, but still requires the updated ffmpeg.

Oh yes, apologies, I am referring to live streams. This is interesting! Thank you... Will look at that today.