If you’re a fan of Appalachia’s “good old-timey music” featured in “O Brother, Where Art Thou?,” “Fiddlin’” will exert a strong appeal. Largely focused on the 2015 Old Fiddlers’ Convention in Galax, Va. — which is billed as the “world’s oldest and largest” and held its 83rd edition in 2018 — the film profiles a large array of fiddlers, pickers, singers, and dancers, emphasizing a bumper crop of young players who are continuing the music’s traditions. Especially winning is jaw-dropping guitar prodigy Presley Barker, who at 11 years old won the adult guitar competition in 2015 (and repeated in 2017). The film features an abundance of performance footage but deftly weaves in interviews with both musicians and fans. After a Q&A with the filmmakers, Barker — now an ancient 14 — will display his astonishing guitar skills live in a post-film concert.