I'm not sure which CPU you have specifically but the lowest-end model of the X1 Carbon Gen3 has an i5-5200U [1] that lists Intel Quick Sync Video support.
From the wiki page for Quick Sync [2]:
> Intel Quick Sync Video is Intel's brand for its dedicated video encoding and decoding hardware core. Quick Sync was introduced with the Sandy Bridge CPU microarchitecture on 9 January 2011 and has been found on the die of Intel CPUs ever since.
I can't confirm but I'd guess your performance issues lie elsewhere than in the h264 decoding specifically.
[1] - https://ark.intel.com/content/www/us/en/ark/products/85212/i...