From Just Solve the File Format Problem
OpenShot is an open-source video editor, originally written by Jonathan Thomas, and later maintained by company named "OpenShot Studios". Its project files have the extension ".osp". Its support for other formats comes from FFmpeg.
OpenShot project files appear to be JSON files, or at least are heavily resemble them; assuming the terminology of the former, the file is a dictionary, with one key (never the first, in testing, and therefore unsuitable for use as a magic number) named "version", whose value is a dictionary with keys "openshot-qt" and "libopenshot", their values being version identifiers.