splitmuxsink add property with start file id

Submitted by m][sko

Link to original bug (#769008)

Description

Created attachment 331840
add_start_file_id_property

I made patch that add property with start file id
Fill free to refactor name, code,...

Patch 331840, "add_start_file_id_property":
0001-splitmuxsink-new-property-start-file-id.patch

Version: 1.9.1