:user!user@user.tmi.twitch.tv PRIVMSG #channel :ACTION message
The trailing part is surrounded by characters with byte value 01, as Matt said. It can usually be matched with \x01 or \u0001 in programming languages.
00000000 3a 75 73 65 72 21 75 73 65 72 40 75 73 65 72 2e |:user!user@user.|
00000010 74 6d 69 2e 74 77 69 74 63 68 2e 74 76 20 50 52 |tmi.twitch.tv PR|
00000020 49 56 4d 53 47 20 23 63 68 61 6e 6e 65 6c 20 3a |IVMSG #channel :|
00000030 01 41 43 54 49 4f 4e 20 6d 65 73 73 61 67 65 01 |.ACTION message.|