Late Crazy Town frontman Shifty Shellshock was sober and happy a few months before his accidental drug overdose ... and seemed committed to staying on the wagon.

TMZ obtained footage from one of Shifty's final interviews before his sudden death, and he was talking sobriety with Mayra Dias Gomes.

The singer -- real name Seth Binzer -- was an invited guest at a Rock to Recovery benefit concert last August at the Fonda Theater in Hollywood, but he made a rare public appearance.

Shifty told Mayra he was sober, happy and feeling good ... explaining how music and his children give him purpose in life.

He also said music was always his therapy, and joked about recovering addicts being the best artists.

Unfortunately, Shifty wasn't able to stay sober ... he was found dead last month and his manager says he died from an accidental drug overdose after mixing prescription drugs with street-purchased drugs.

As we first reported ... Shifty's friend and sober coach, Tim Ryan, says he was living in a tent in downtown L.A.'s MacArthur Park after relapsing, and was homeless when he died.