I recently upgraded from Ubuntu 16.04 LTS to 18.04 LTS "Bionic Beaver". Then I noticed that online video playback can "freeze" for several seconds (can be tens of seconds) every now and then, while sound is still playing. Then video playback resumes from new position, synchronized with sound.
I thought it's a network-related problem, but then I experienced the same problem during the local video file playback using VLC player. I tried all solutions at this forum, including disabling Gnome extensions and changing kernel settings, but there was no even a slightest improvement. 16.04 LTS had no such problems.
My system is
Lenovo B51-80 with
Intel Core i5 CPU,
8Gb RAM and
AMD Radeon R5 M330 graphic card (which has no official Ubuntu 18.04 drivers, so default open-source wrapper utilizing CPU's built-in Skylake GPU is used). Also I use SSD for root file system and HDD (7200 rpm) for home and var ones.