Voip and video conference/video call type facilities are not real time, they nearly are, but not quite, especially across the internet.

It might be possible to set Quality of Service (QoS) in your router to prioritise the appropriate protocols, but... The compression algorithms in the codecs are also somewhat lossy. The sheer quantity of data in the music and video will not be helping. In addition, many ISP's reduce priority on Voip and video call data that are not generated by services they directly provide - this could be happening anywhere along the data link.

The other thing to note is that packets containing this kind of data are not guaranteed to be delivered. If packets get out of order or dropped somewhere along the way they are not resent, the philosophy being that maintaining the flow of data in a timely fashion is more imnportant than data accuracy so missed packets stay missed.

Have you found that some times of day are better than others? If so, this could indicate that system load outside your home services could be where the real problem lies.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!