SAN FRANCISCO — Apple Inc. CEO Steve Jobs returned Wednesday to the showman role that has helped define his company leadership, taking the stage for the first time since his medical leave to announce such new products as an iPod Nano that records video.

Jobs, who had a liver transplant this spring from a young adult who died in a car accident, got a vigorous standing ovation from many in the audience.

Looking thin and speaking quietly and with a scratchy voice, the 54-year-old CEO urged everyone to become organ donors.

“I wouldn’t be here without such generosity,” Jobs said.

Jobs had not appeared at such a product launch event since last October. He bowed out of his usual keynote at the year’s largest

Mac trade show in January and went on leave shortly thereafter for nearly six months.

At an event for journalists, bloggers and software partners, Jobs announced updates to Apple’s iTunes and iPhone software and unveiled a new iPod Nano with a built-in video camera.

Jobs, whose medical problems began more than five years ago and included treatment for a rare form of pancreatic cancer, seemed happy to be back in the spotlight, saying, “I’m vertical, I’m back at Apple and loving every day of it.”

Apple compared the new video-camera Nano to Cisco Systems Inc.’s Flip Mino, a tiny, simple video recorder that sells for $149, just like the basic, eight-gigabyte version of the overhauled Nano (The 16 GB Nano costs $179). The Nano — the smallest iPod that has a screen — also has a microphone, a pedometer, a 2.2-inch display and an FM radio tuner.

Meanwhile, the new version of iTunes, known as iTunes 9, gives people more control over what content gets loaded on to iPods and iPhones. It lets five computers on the same home network share — by streaming or copying — music, video and other content, a departure from the strict copy protection Apple insisted on in the past.