fix wrong timescale used to calculate fps

[nkming2]

fix #3436

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.87%. Comparing base (7ac25bb) to head (d619a1f).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/quicktimevideo.cpp	54.54%	1 Missing and 4 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3437   +/-   ##
=======================================
  Coverage   64.87%   64.87%           
=======================================
  Files         114      114           
  Lines       21671    21673    +2     
  Branches    10652    10652           
=======================================
+ Hits        14059    14061    +2     
  Misses       5391     5391           
  Partials     2221     2221           

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