Shia LaBeouf is showing off his acting talents ... and his fully naked body in the new music video for Icelandic indie band Sigur Ros.

The 26-year-old Transformers actor goes full-frontal in a video for the song "Fjogur Piano" ... that's been described as a "never-ending cycle of addiction."

Aside from dropping his pants for music videos, Shia will be appearing alongside Tom Hardy, Jessica Chastain, Guy Pearce and Gary Oldman in the upcoming western flick Lawless.