I Know that Voice is a documentary about voice actors narrated by voice actors. With very few exceptions (Matt Groening, director Andrea Morano, writer David X. Cohen, and a few others), everyone who appears onscreen in the film is a voice actor. They're not just single character actors, either. These are actors who can appear onscreen every time with a different caption under their name indicating a different credit. The film is a tribute to voice acting as a craft and business. The actors discuss creating voices, developing characters, interpreting scripts, getting work, and keeping a job among many other subjects. It's a conversation created through dozens of actors discussing voice acting through their own lens of experience.
The thing you'll immediately notice is the joy. These actors love what they're doing. They're passionate about what they do. They know how fast a job can go away and they choose to keep moving forward. Pamela Segall, for example, discusses a hypothetical of fitting in great at Cartoon Network but not actually working at Cartoon Network. She's brought in for an hour every other week to fill in various characters and has no guarantee of ever being called in again.
Even more interesting is one of the longer segments in the documentary. A series of voice actors all show off how they can voice some of the classic Looney Tunes characters, like Bugs Bunny and Porky Pig. There's even a voice acting teacher who breaks down the actual speech pattern for Porky Pig.
The point is the actual role of the voice actor. It's not just creating a funny voice. A few actors point out that celebrities who do cartoon voices are often just asked to read the script so people recognize the voice. That's different than being hired to turn a drawing and a script into a character that can be sustained for an episode, let alone a feature film or years of a TV show.
I Know that Voice doesn't dwell too long on any single topic. A section called "Anime" quickly abandons the challenge of lip dubbing to discuss the myriad of Star Wars animated properties and the challenge of voicing multiple characters.
The film deserves a lot of credit for pulling so many different voice actors together for a documentary about voice acting. I can watch and ask "why not x, y, or z?" but that's beside the point. This is a celebration of the artistry and the industry. It's just fascinating to watch the people behind the animation we love so much discuss how it actually works.