When you clone a repo on github that contains a submodule, update the submodule with the following command.git submodule update –remote –merge

If you can’t update, try re-adding the submodule, for example:

git submodule add https://github.com/cisco/openh264 open_source_code/openh264

Keeps giving the following error.
‘open_source_code/openh264’ already exists in the index

Run the following command to fix the problem.

git rm -r --cached open_source_code/openh264