For video playback reviewing, actually everything is handled by the GPU,
You can decode up to 4K in youtube and you wont even hear the fan is ramping up or system become hot
measuring the gpu wattage might be more meaningful in this way


since VP9 on youtube already supported by modern GPU, you wont see any gpu utilization in Task Manager, unless you change the setting
to really stress what the system capable of, you can turn off the hardware acceleration in chrome, restart the browser and you will see the 4K video bring down the cpu to its knee.
software decoder(ffmpeg based) in chrome or chrome base browser still far from efficient.