In Johannesburg, South Africa, we follow two young factory workers through an ordinary day on and off the job. “Casual Workers,” directed by Keagan Afonso, is a free roaming portrait, a day in the life. Periods of work are followed by periods of rest and leisure, smoking cigarettes, staring at the clouds, freestyle rapping, et al. The natural personalities of its performers — Nala Tshibubudze and Tebogo Chakela — carry the film; they are captured in spontaneous compositions and fleeting exchanges, lively conversations about language and culture lead into periods of reflection and solitude. It’s a self-assured piece of abstract storytelling, rich in tone.