"Walk the Line" was solid, with great performances from its two leads, but the 60-minute documentary "Johnny Cash Live at San Quentin" is the kind of thing that shows how pointless the Hollywood biopic is. Who needs Joaquin Phoenix and Reese Witherspoon when you can watch the real deal at the intimate Trylon? While most fans know about Cash's legendary performance at Folsom Prison in 1968, this performance, shot the following year and directed by Michael Darlow, is the rarer treasure. Thankfully, Sound Unseen continues to unearth these musical gems for lucky Minnesota moviegoers. Cash is full of energy throughout the San Quentin concert, giving his all for the inmates and clearly feeding off their love of his songs. When June Carter Cash shows up for a few numbers, the look of fear in her eyes is priceless. But it's the insightful interviews with prison guards and prisoners that make this more than the typical concert doc. Their stories are almost more engaging than Cash's music. Almost.