Inconsistancy.  The number of frames per region is not constant.
 1         11         50

 1         11         23
 2         24         50

 1       4101         11         23         35         47
 1       4102         12         24         36         48
 1       4103         13         25         37         49
 1       4203         14         26         38         50
 1       4202         15         27         39
 1       4299         16         28         40
 1       4300         17         29         41
 1       4393         18         30         42
 1       4392         19         31         43
 1       4391         20         32         44
 1       4298         21         33         45
 1       4201         22         34         46