What could be the reason for some videos on YouTube be unwatchable and almost freezing Chromium (even when paused!) while others play fine at a the same quality, and same codec (avc1, opus). For example videos from Formula 1 channel play fine at 360p without frame drops and with rare frame drops at 480p, but some other videos ("Gabber Dance" from channel "one medium films") for example drop 99% frames (but audio plays okay), the rest of page struggles to load, and even when paused the CPU is at 100% use. Both videos use avc and opus codecs, not vp8 or vp9. adblock with one filter list is installed in this old laptop and acceptable adds are also blocked.
Information about the system: Debian 9.6 Lxde 32bit with non-free Intel graphics drivers for GMA 900, latest version of Chromium (71. something), Adblock. Pentium M 1.73Ghz, GMA 900 GPU with 128MB shared RAM. 1.5 GB system RAM. Full laptop specs: https://www.cnet.com/products/fujitsu-lifebook-c1320d-15-4-pentium-m-740-win-xp-pro-2-gb-ram-80-gb-hdd-series/