Yes, there is a Bob Marley documentary that's coming out on 4/20. I'll let you make your own joke there.

Yes, there is a Bob Marley documentary that’s coming out on 4/20. I’ll let you make your own joke there.

If you’re making “Marley” part of your, ahem, festivities that day, you should know this. The movie is two and a half hours long and is actually a thorough and engaging documentary … not really a party movie.

Director Kevin MacDonald (“The Last King of Scotland”) sets out to make the definitive Marley documentary. I don’t claim to be enough of an expert to know his major competition, but this is fine biography filmmaking.

Through stock footage and — most engagingly — interviews with those close to the man himself, MacDonald lovingly tells the tale of Marley’s rise. His humble beginnings are more humble than most, and the social and political landscape of Jamaica loom large in the film.

Of course, this is an ambitious tale to tell. You have the rise of not only the man who would become — wait for it — “Legend”-ary, but of reggae music at large. And therein lies the rub.

It’s hard to find much wrong with MacDonald’s storytelling, but that runtime can feel lengthy … especially for a documentary as interview-oriented as this.

Even casual fans will admire the craftsmanship. For hardcore fans, this should be a no-brainer. Just plan your smoke breaks accordingly.