[FFmpeg-user] fieldmatch, documentation submission

[Mark Filipak]

This is my first submission for improved documentation -- Paul Mahol asked that I post suggestions 
to this mailing list.

The diagrams below are for 'fieldmatch'.

I believe they are an inprovement for two reasons: 1, Letter tokens (lettered fields) are more 
understandable -- easier to correlate -- than the current number tokens, and 2: The matching step is 
explicitly shown.

fieldmatch=field=top:mode=pcn
    tff
   /
[A+a][B+b][B+c][C+d][D+d]
_____M_A_T_C_H_I_N_G_____    __R_E_A_R_R_A_N_G_I_N_G__
[A a]                     -> [A+a]
      [B b]                ->      [B+b]
         b [B  ]           ->           [B+b]
              c [C  ]      ->                [C+c]
                     [D d] ->                     [D+d]
  c    c    p    p    c       [A+a][B+b][B+b][C+c][D+d]

fieldmatch=field=top:mode=pcn_ub   (ub pass following failed pcn pass)
[A+a][B+b][B+c][C+d][D+d]
_____M_A_T_C_H_I_N_G_____    __R_E_A_R_R_A_N_G_I_N_G__
[A a]                     -> [A+a]
      [B b]                ->      [B+b]
           [  c] C         ->           [C+c]
                [  d] D    ->                [D+d]
                     [D d] ->                     [D+d]
  c    c      u    u  c       [A+a][B+b][C+c][D+d][D+d]
              ^----^------ mimic field=bottom because pcn pass failed


fieldmatch=field=bottom:mode=pcn
    bff
   /
[a+A][b+B][c+B][d+C][d+D]
_____M_A_T_C_H_I_N_G_____    __R_E_A_R_R_A_N_G_I_N_G__
[a A]                     -> [a+A]
      [b B]                ->      [b+B]
           [c  ]   C       ->           [c+C]
                [d  ]   D  ->                [d+D]
                     [d D] ->                     [d+D]
  c    c    n    n    c       [a+A][b+B][c+C][d+D][d+D]

fieldmatch=field=bottom:mode=pcn_ub   (ub pass following failed pcn pass)
[a+A][b+B][c+B][d+C][d+D]
_____M_A_T_C_H_I_N_G_____    __R_E_A_R_R_A_N_G_I_N_G__
[a A]                     -> [a+A]
      [b B]                ->      [b+B]
       b   [  B]           ->           [b+B]
            c   [  C]      ->                [c+C]
                     [d D] ->                     [d+D]
  c    c      b    b  c       [a+A][b+B][b+B][c+C][d+D]
              ^----^------ mimic field=top because pcn pass failed