Remember that audio is being trancoded using the CPU, so a spike in usage is to be expected, unless you have a device that can direct play the spesific audio format.
You could post a log, but a quicker answer is to simply click on the gear icon in the lower right corner when playing a video, and selecting playback info, it will state there if it is direct playing or transcoding.
you might have to lower the bitrate to force transcoding.
EDIT: If you have the option, you should return that B580 and opt for buying an older Arc A310/A380, they have the exact same media encoders in the silicon, the B580 is just a waste of money and energy.
Besides that, the Arc A series should have the low power encoder options set, the B580 should be no different one should think.
You could post a log, but a quicker answer is to simply click on the gear icon in the lower right corner when playing a video, and selecting playback info, it will state there if it is direct playing or transcoding.
you might have to lower the bitrate to force transcoding.
EDIT: If you have the option, you should return that B580 and opt for buying an older Arc A310/A380, they have the exact same media encoders in the silicon, the B580 is just a waste of money and energy.
Besides that, the Arc A series should have the low power encoder options set, the B580 should be no different one should think.