Regex :

/^\s*\d+\s*$(?:\r?\n?)+^\s*([\d:,.]+)\s*-->\s*([\d:,.]+)\s*$(?:\r?\n?)+((?:.(?:\r?\n?)?)?)(?:\r\n|\r|\n|$)/gm;

Test String : 1 00:00:02,070 --> 00:00:8,572 ( explosion and number of members )
( inaudible radio chatter )