How to check when merging of formats gets completed?

[Elite]

When importing youtube-dl we have progress_hook to get download status, but how to know when format merging has finished?

[SleepProgger]

I just had the same problem.
But, if you think about it: merging has finished when the download/extract_info/... function returns.
To get the final filename F.E: use:

info = ydl.extract_info(url, download=False)            
ydl.process_info(info)
print "Filename %s" % info['_filename']

Or use prepare_filename(info)