John Wells made sure his adaptation of "August: Osage County" stayed faithful to Tracy Letts' Pultizer Prize-winning text. "We counted, and there were only six or seven lines of dialogue which are not in the play," Wells, best known for "ER" and "The West Wing," told HuffPost Entertainment in a recent interview. "Some of the scenes, in fact, were put in a new location, but we actually pulled dialogue from the play to put into the scenes."

Written for the screen by Letts himself and directed by Wells, "August: Osage County" tells the story of the Weston family -- among them Meryl Streep as the Weston's matriarch and Julia Roberts as her eldest daughter -- and how the group deals with the death of their patriarch after years of long-simmering anger and resentment. But it's funny.

"Hopefully, you're laughing and it kind of hurts," Wells said when asked about the darkly comic nature of his film. "There is a guilty feeling of all the times you laughed at your own dinner table or at your own siblings' expense. Or when you were at the butt of the joke, and you had to laugh as if you thought it was funny, but you didn't really think it was funny. I think that propels a lot of it and makes it work."

Wells spoke to HuffPost Entertainment about the pressures of adapting "August: Osage County" and why one role in particular proved so difficult to cast.

This play is very funny, but maybe not in the way audiences are expecting. How difficult was it to maintain that kind of tone?
The danger is always -- and Tracy has talked about this -- that there have been a lot of wonderful adaptations of plays that were very funny on stage, but when adapted on screen, lost that sense of humor. Some of that is just the medium of cinema. It's a very realistic medium. Some things don't seem as funny when you're seeing them in the context of the real thing. I was very conscious of it. I grew up in a family that was very barbed and difficult, and there was a lot of humor. None of it was painless humor. All of it was at someone else's expense. It was kind of always about power. When I saw the play and we started working on it, it was very familiar to me, including really long dinners at my house with excruciatingly long graces. So it wasn't hard to do, but the concern was would the audience know that it was funny? You're hoping that by the time the movie is marketed, that people kind of have a general sense of what to expect when they come, but when we were doing the first test screenings and the first festival screenings, we didn't know if anybody was going to laugh. I literally just sat there, like, "Dear God, please laugh." So a lot of our adjustments were musical adjustments, timing adjustments. Like, is this musical cue making it harder for people to understand? How do we give subtle cues to the audience that they can laugh?

Were you nervous about being the person to adapt this Pulitzer Prize-winning play?
I was excited and terrified. The thing that is exciting is that you know it works. The thing that is terrifying is that you know it works. If it doesn't work, you're the reason it didn't work. Nobody is pointing at anybody other than you! I loved the play. I saw it in the theater before I knew I was even going to be involved. I consider it to be one of the great American plays. I think it's going to be performed for 100 years. I think it'll be one of those pieces: our generation's great American family drama. So I was worried that I was going to be the guy who screwed that up. "Don't go see the movie, see the play! The movie is terrible." I didn't want to be that guy. Normally when you go in to work on a piece of material, you are trying to figure out whether the scenes are working. In this case, you knew it worked. The actors knew it worked. There was no questioning the text, which was great. So that's the advantage. You're going into scenes, and you're thinking, "If the scene's not working, it's not working because we haven't figured it out and not because the basic material doesn't work." I have a friend with a wonderful saying I like to use: The script is innocent until proven guilty. In this case, the script had a Pulitzer Prize behind it.

Directors have often said that casting is their most important job, and you've put together a murderer's row of talent here. How did you go about that?
You're right to say first that the most important thing you can do as a director is casting. That's a battle. It's a bit of a battle because you're trying to get the right mix, particularly for a family. And you want to mix acting styles correctly. People approach the work in different ways. You want to make sure no one wants to kill each other because the approach is different. That was the big battle. I love actors and I love working with ensembles, so I just love that whole process. People say to me, "Well, how do you direct Meryl Streep?" You're not wandering over to Meryl telling her how to act. She's an extraordinary talent and unbelievably hard working; she works harder than anyone I have ever worked with before. But I use this analogy: It's more like being a conductor of a really strong chamber orchestra. You have these musicians -- they are fabulous on their instrument and they know how to play it. So I'm not going to tell them how to play, but I am completely responsible for making certain that the whole, as a whole, has a sound. That it has a shape that I want.

Julia, in particular, is incredible, especially in a role that not many people might expect to see her play.
Julia, when we first started talking about it, that was our question. This is an embittered, angry woman in her mid-40s, and it's going to be a lot of time spent not being a very nice person. Julia has a screen persona that she has not exclusively done, but done often, where people sort of expect her to be a certain way. None of that was going to be what we're doing. She said, "Yeah, that's exactly why I want to do it." A lot of our conversations on the set were about me just saying, "No, she's angry about this. She's angry about that. This is about that." Julia got it. The performance lacks any vanity. The clothing. She wore no makeup. Her hair. She put on a little extra weight for it. This is a woman whose husband has left her and she hasn't gotten to that stage that women usually go through where they get really great and the husband sees them and goes, "You look fabulous!" She's in the depression period of barely wanting to shower.

Which role was the hardest to cast?
Ivy. It's a really difficult role.

How many people did you see?
70? 50? Wonderful actors, many of whom I admired and worked with before. You needed someone who is the naturally beautifully woman, but who has clearly kept it under wraps. It's not part of her persona and she doesn't see herself sexually. She moves through life in a way that you don't notice her. Yet you can see who she should have been.

What stood about about Julianne Nicholson, who plays Ivy?
I worked with Julianne before. She came in and did this audition, toward the end of the casting process. She was doing a Sam Shepard play and hadn't been available to audition. She came, and it was second or third to the end of the days we were seeing people. We saw people for six months. Then I felt guilty, because I had known her and worked with her before.

This is a Tracy Letts play. He's won awards for this play.
Tracy is set. He's got the Pulitzer, the Tonys.

If this film doesn't win an Oscar would you be disappointed?
You can't control it. I don't mean to sound nonchalant about it, because I don't feel nonchalant about it. The only thing you can control is trying to do it as well as you can possibly do it. I was very fortunate in all of my career in television to have a lot of things that received a lot of awards recognition. I'm very aware of "the thing." It's not about validation. It's a smaller film; it has major stars but it's a smaller film. It's not going to have a $60 million marketing budget, like a major studio film. Any kind of awards recognition means more people see the work. At the base of this, I come out of doing theater. I worked at La MaMa. I did lots of shows where you peered out from the curtain and there were 12 people watching. You just want more people to see it. You work really hard for long period of time. It's not like digging ditches, but it's hard work. You do it a lot of hours. You put a lot into it. You just want people to see it. So any kind of recognition -- whatever sort of form that recognition takes. Somebody says, "Oh, I heard about that. I should go see it. I heard it's good."

I'm not trying to diminish the power of critics, either, because I think they're useful. But truthfully, people get their information from so many different places, that any kind of recognition -- and people have so many different choices about what to watch and do with their leisure time -- any validation from anywhere makes a huge difference in how many people come and see the film.

"August: Osage County" opens in limited release on Dec. 27.

This interview has been edited and condensed.

Also on HuffPost:

Loading Slideshow...
  • Chris Cooper Benedict Cumberbatch

    This photo provided by The Weinstein Company shows Chris Cooper, left, as Charles Aiken, and Benedict Cumberbatch, as "Little" Charles Aiken, in a scene from the film, "August: Osage County." What will draw Northeast Oklahomans to theaters next month to see the film, will be the storefronts, streets and markings of the place they call home used as a location for the film, based on the Pulitzer Prize-winning play by Oklahoma native Tracy Letts. It was shot in and around Osage County, including Pawhuska and Barnsdall. (AP Photo/The Weinstein Company, Claire Folger)

  • DERMOT MULRONEY

    This photo provided by The Weinstein Company shows Dermot Mulroney as Steve in a scene from the film, "August: Osage County." What will draw Northeast Oklahomans to theaters next month to see the film, will be the storefronts, streets and markings of the place they call home used as a location for the film, based on the Pulitzer Prize-winning play by Oklahoma native Tracy Letts. It was shot in and around Osage County, including Pawhuska and Barnsdall. (AP Photo/The Weinstein Company, Claire Folger)

  • Juliette Lewis

    Juliette Lewis arrives on the red carpet at the 2013 AFI Fest premiere of "August: Osage County" at the TCL Chinese Theatre on Friday, Nov. 8, 2013 in Los Angeles. (Photo by Chris Pizzello/Invision/AP)

  • George Clooney, Grant Heslov

    Producers George Clooney (R) and Grant Heslov arrive at the 2013 AFI Fest screening of "August: Osage County" at the TCL Chinese Theatre on Friday, Nov. 8, 2013 in Los Angeles. (Photo by Paul A. Hebert/Invision/AP)

  • Julianne Nicholson

    Actress Julianne Nicholson arrives at the 2013 AFI Fest screening of "August: Osage County" at the TCL Chinese Theatre on Friday, Nov. 8, 2013 in Los Angeles. (Photo by Paul A. Hebert/Invision/AP)

  • Chris Cooper arrives on the red carpet at the 2013 AFI Fest premiere of "August: Osage County" at the TCL Chinese Theatre on Friday, Nov. 8, 2013 in Los Angeles. (Photo by Chris Pizzello/Invision/AP)

  • Juliette Lewis, Dermot Mulroney

    Juliette Lewis and Dermot Mulroney arrive on the red carpet at the 2013 AFI Fest premiere of "August: Osage County" at the TCL Chinese Theatre on Friday, Nov. 8, 2013 in Los Angeles. (Photo by Chris Pizzello/Invision/AP)

  • AFI FEST 2013 Presented By Audi Premiere Of The Weinstein Company's "August: Osage County" - Red Carpet

    HOLLYWOOD, CA - NOVEMBER 08: Actress Julianne Nicholson attends the premiere of The Weinstein Company's 'August: Osage County' during AFI FEST 2013 presented by Audi at TCL Chinese Theatre on November 8, 2013 in Hollywood, California. (Photo by Kevork Djansezian/Getty Images for AFI)

  • Julia Roberts

    Julia Roberts arrives at the premiere of "August: Osage County" on day 5 of the Toronto International Film Festival at the Roy Thomson Hall on Monday, Sept. 9, 2013, in Toronto. (Photo by Evan Agostini/Invision/AP)

  • AFI FEST 2013 Presented By Audi Premiere Of The Weinstein Company's "August: Osage County" - Red Carpet

    HOLLYWOOD, CA - NOVEMBER 08: Director John Wells and guest attend the premiere of The Weinstein Company's 'August: Osage County' during AFI FEST 2013 presented by Audi at TCL Chinese Theatre on November 8, 2013 in Hollywood, California. (Photo by Kevork Djansezian/Getty Images for AFI)

  • Julia Roberts

    Julia Roberts arrives at the premiere of "August: Osage County" on day 5 of the Toronto International Film Festival at the Roy Thomson Hall on Monday, Sept. 9, 2013, in Toronto. (Photo by Evan Agostini/Invision/AP)

  • AFI FEST 2013 Presented By Audi Premiere Of The Weinstein Company's "August: Osage County" - Red Carpet

    HOLLYWOOD, CA - NOVEMBER 08: Actress Carrie Coon and writer Tracy Letts attends the premiere of The Weinstein Company's 'August: Osage County' during AFI FEST 2013 presented by Audi at TCL Chinese Theatre on November 8, 2013 in Hollywood, California. (Photo by Kevork Djansezian/Getty Images for AFI)

  • 17th Annual Hollywood Film Awards - Show

    BEVERLY HILLS, CA - OCTOBER 21: Actress Julia Roberts accepts the Hollywood Supporting Actress Award for 'August: Osage County' onstage during the 17th annual Hollywood Film Awards at The Beverly Hilton Hotel on October 21, 2013 in Beverly Hills, California. (Photo by Mark Davis/Getty Images)

  • 17th Annual Hollywood Film Awards - Show

    BEVERLY HILLS, CA - OCTOBER 21: Actress Julia Roberts accepts the Hollywood Supporting Actress Award for 'August: Osage County' onstage during the 17th annual Hollywood Film Awards at The Beverly Hilton Hotel on October 21, 2013 in Beverly Hills, California. (Photo by Mark Davis/Getty Images)

  • 17th Annual Hollywood Film Awards - Show

    BEVERLY HILLS, CA - OCTOBER 21: Actress Julia Roberts accepts the Hollywood Supporting Actress Award for 'August: Osage County' onstage during the 17th annual Hollywood Film Awards at The Beverly Hilton Hotel on October 21, 2013 in Beverly Hills, California. (Photo by Mark Davis/Getty Images)

  • "August: Osage County" Press Conference - 2013 Toronto International Film Festival

    TORONTO, ON - SEPTEMBER 10: Actress Julia Roberts attends 'August: Osage County' Press Conference during the 2013 Toronto International Film Festival at TIFF Bell Lightbox on September 10, 2013 in Toronto, Canada. (Photo by Jason Merritt/Getty Images)

  • "August: Osage County" Press Conference - 2013 Toronto International Film Festival

    TORONTO, ON - SEPTEMBER 10: Actress Julia Roberts attends 'August: Osage County' Press Conference during the 2013 Toronto International Film Festival at TIFF Bell Lightbox on September 10, 2013 in Toronto, Canada. (Photo by Jason Merritt/Getty Images)

  • "August: Osage County" Press Conference - 2013 Toronto International Film Festival

    TORONTO, ON - SEPTEMBER 10: Actress Julia Roberts attends 'August: Osage County' Press Conference during the 2013 Toronto International Film Festival at TIFF Bell Lightbox on September 10, 2013 in Toronto, Canada. (Photo by Jason Merritt/Getty Images)