When an x264 option doesn't include a "=", it is silently ignored. This
is frustrating for users. Log when part of the options string is
ignored.
Aside from logging, this commit should not change behavior.
We do a bad job of handling errors in user-supplied x264 options. I want
to improve our error handling. To make my job easier, move the code for
parsing the x264 options string into its own function. Also, add some
tests for the functionality.
Aside from a minor tweak to a log message for the opencl option, this
commit should not change behavior.
