[FFmpeg-trac] #10017(documentation:new): Filter expression syntax is undocumented

[FFmpeg]

#10017: Filter expression syntax is undocumented
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             Reporter:  jason        |                     Type:  defect
               Status:  new          |                 Priority:  important
            Component:               |                  Version:
  documentation                      |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 Multiple filters take a mathematical expression as a parameter, for
 example 'setpts' and 'select'.

 The syntax of this expression is completely undocumented, despite its
 heavy use. For example, what functions are available? Are boolean
 combinations allowable and if so, what are the operators? What other
 mathematical operators are available? Are there equality comparison
 operators?

 Afaict there is no hint in any of the documentation of the format of an
 "expression".

 If it does exist, it should be made available under a more obvious
 documentation section heading, and possibly moved towards the beginning of
 the filter docs with the rest of the general common filter info.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10017>
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