Jack Black describes Frank or Francis to MTV News:

"[The script is] under lock and key. It is a musical," Black shared. "I will be singing. Everyone will be in fact. If you're in that movie you will be singing. There's no just regular talking it's all [singing]."

[...] "That might not be the case," he continued. "Don't quote me on that."

[...] "Erase that part. I gotta go back and read the script again. Maybe there is some regular talking mixed in. In fact, there is," he finished. (Source)