The $insong.length and $insong.pos dont return the correct song lengths. I used $insong.length and $sound().length and got different responses. The longer the song is, the bigger the difference. I am using mIRC 6.16
I've experienced this A LOT with mp3s that have a variable bitrate. I reported this once here, but I never really knew if it was an issue with Windows Media Player or mIRC.