With clients that cannot natively display certain subtitle formats, plex must burn them before the final render stage and that’s fine. I also understand that is essentially a software process, even with hardware transcoding enabled. What I do not understand is why I can transcode from an SDR 1080p/30Mbps source to a 4Mbps stream with subtitles burned at a rate of 7.0-8.0x. But doing so with an HDR 2160p/100Mbps source to the same 4Mbps stream cannot even sustain 0.8x.
Do burned subtitles force the HDR:SDR tone mapping to software mode? If so, why and how can this be fixed?
4x the pixel count to deal with for 2160p vs 1080p.
And you have 3x the bitrate.
It probably uses the more complex HEVC rather than AVC encoding scheme as well which is heavier on processing load.
You are talking about a huge glut of data processing request.
Tone mapping in my experience uses relatively little processing power.
You are just struggling with a massive large and complex data stream.
On top of that, you haven’t mentioned anything about subtitles, are you using image based subtitles? that’s even more pixels to manage, and why merging them is process intensive. Text based subtitles are basically free of cpu cycle use. You’d probably better better off putting your subtitles in easy to use text format.
