To build a version that can handle 8 bit, or 10 bit, or 12 bit videos, a patch is provided in the thirdparty subdirectory that needs to be applied to do so. Be aware that the compile may take more time and seems to be about twice as long. To apply the required patch:
cd /path/to/cinelerra-5.1/thirdparty patch < compile_multibit_X265.txt mv x265_3.5.patch* src/.
The CINELERRA-GG Community, 2021