So, here's the situation. I have a Ryzen 5800X CPU. Whenever I watch a 4K youtube video (VP9 codec, Mozilla Firefox, no GPU acceleration, decoded and rendered solely by the CPU) with the ACPI_CPUFREQ driver the power consumption stays around 50-55 Watts while the CPU is constantly hitting or staying around the maximum turbo frequency (~4.75GHz). Whenever I disable Turbo Boost (echo 0 > /sys/devices/system/cpu/cpufreq/boost), the power consumption instantly deceases to around 39W with no difference in video decoding, i.e. frames are not dropped, decoding is smooth and steady. We are talking about a staggering 30% decrease in power consumption just by disabling Turbo Boost and limiting CPU frequency to 3.8GHz. I suppose this is not right and should be fixed/addressed. I'm using the ondemand governor with default settings.
This is reproducible for other CPUs as well. Watching HW accelerated videos in Firefox results in ~40% higher power consumption than necessary to actually play them.