У вашего броузера проблема в совместимости с HTML5
UPDATE!
Do not buy this mixer if you are using it in combination with a Mac and 10.13 High Sierra. Mine is not working anymore and Pioneer knows about this problem and does not support anything since months!
This means, the Mixer will not be shown as an external sound card in your system and no DVS or other functions are possible in some cases.
preview of the Pioneer DJM 250 MK2 Mixer.