SUMMARY
Speech to text on MacOS not finding path to ffmpeg.

STEPS TO REPRODUCE
Select clip > Speech Editor > Start recognition

OBSERVED RESULT
Reports error: No speech detected with log:
FileNotFoundError: [Errno 2] No such file or directory: 'ffmpeg'

EXPECTED RESULT
Speech recognized :O)

SOFTWARE/OS VERSIONS
macOS: 12.3.1

ADDITIONAL INFORMATION
Determined that when editing the file and adding the folder that ffmpeg is in to the path that it works.
I don't know where the PATH should be set for these scripts, so this probably isn't the ultimate fix, but it got the job done in this case.
1. Edit the file /Applications/kdenlive.app/Contents/Resources/scripts/speechtotext.py
2. Add on around line 18 the following code:
    if sys.platform == 'darwin':
        os.environ["PATH"] += os.pathsep + '/Applications/kdenlive.app/Contents/MacOS'