Did only Arjun perceive Bhagwat Geeta?

 Bhagwat Geeta was preached by Vasudev Krishna to Arjun. But the story has something else that there were 3 other peoples listening to Geeta. They were Hanuman, Sanjay and Barbarik.

Hanuman

Hanuman was one of the cheeranjivies( immortal). He was from Treta yug to till now in this world but somewhere else. In treta yug, He was the greatest devotee of Ram so met lord Krishna in Dwapara yug who was the next incarnation of lord vishnu after lord Ram. Hanuman knew the story about Krishna and met with him. Hanuman requested lord Shri Krishna to preach him more knowledge. At mahabharata war Hanuman was set on the flag of chariot of Arjun and Krishna.

Sanjay

Sanjay had the power of divine eyesight " Divya dristi "which was granted by sage Byas. He was the messenger of Hastinapur. He narrated to Dhritarastra the events at Kurukshetra during war. He saw and listen all the Geeta from Shri Krishna.

Barbarik

Barbarik is the only one who saw the Mahabharata war from the first day to last. His head was placed on the top of the mountain near the battlefield by Shri Krishna as a Guru Dakshina. He listened all the Geeta from there.