Sweet romantic comedies aren’t my thing. I much prefer murder and mayhem, action and terror, but watching “Begin Again” my mouth involuntarily curled up in a smile — a goofy smile, like when I see puppies and babies. For the 104 minutes of romcom my face stayed like that. Aside from wishing she’d eat something, I’ve always liked Keira Knightley and my movie crush on Mark Ruffalo began with “Zodiac.” He looks dreadful in this movie, though. Adam Levine (Maroon 5 and TV’s “The Voice”) plays Knightley’s Ken-doll handsome boyfriend. He looks great until he shows inexplicably grows a mountain man beard. Hock ptooey.Producer Judd Appatow and Irish writer director John Carney (“Once”) made Ruffalo’s Dan a mess. He’s a boozing loser estranged from his wife (Catherine Keener) and teen daughter (Hailee Steinfeld). And his record-label partner Saul (Mos Def) is ready to throw him out on his ass-pirations.Gretta (Knightley) is a singing and guitar-playing songwriter who has a joyfully romantic relationship with Dave (Levine). But, after five years together, he takes off on newly found fame and leaves her in the dust. She figures out that he is cheating on her when he gets back from L.A. and plays a new song to her in their kitchen. Perhaps she’s psychic because there were no lyrics that actually indicated that. It was one of those oddball movie moments where you go, “Huh?” But whatever, you just say, “OK,” and move on.Gretta crumbles onto her guitarist friend Steve’s couch.

Steve is played perfect pitch by Teddy-bear-ish and plump James Corden. Gretta turns to Steve’s computer and orders a ticket home to England but Steve drags her out to join him one last time onstage before she goes. “I don’t want to come home and find you with your head stuck in the oven,” he says. Gretta goes, albeit reluctantly, and ends up coaxed onto stage where she plays a mournful tune that she magically just wrote about her romance going kaput. You know how these things go in movies, people don’t have to work at writing or editing, their first drafts are right on time. Meanwhile, a drunken and ready-to-lay-down-and-die Dan hears her singing along with her acoustic guitar and his head lifts up from his liquor and self-pity. Here’s my favorite part. It’s a marvelous bit of cinema where Dan imagines full music accompaniment. Guitars stand up and twirl, pianos and violins play, his head is filled with an imagined album and he gets a glimmer of hope that life may be worth living. Dan approaches Gretta and says he wants to make a record with her. Unlike every musician I’ve ever known who’ve always had their tongues hanging out for just such an unlikely moment, Gretta is rather blasé about it. Not because of her depression, but because she is somehow above corrupting her music by making it in any way a commercial venture.As ridiculous as all of this sounds I was soaking it all in and loving it. It’s a silly fable but with incredibly likable characters and a full musical score that held my attention. I can’t even say I remember a single tune from it but I enjoyed it just the same. And a cameo by CeeLo Green in a bathing suit by a huge pool and playing a grateful movie mogul is great fun.

“Begin Again” is now available on Blu-ray, iTunes, and DVD.