Immersive audio and HDR formats are the ways in which a film's sound and picture are recorded, so that sound can come from all around and above the audience, and the picture can show brighter highlights and deeper shadows. Immersive audio is also called 3D audio or object-based audio. HDR is short for high dynamic range. Dolby Atmos and Dolby Vision are the best-known examples. The companies that own these formats license them to the makers of cinema equipment, TVs, soundbars and phones, and earn a fee for each device.
How is immersive audio different from ordinary surround sound? Older surround sound fixes each sound to a channel, such as the front-left speaker or the rear-right speaker. In immersive audio, each important sound is an object with a position in 3D space. The film's file stores the sound and its position, moment by moment. The equipment in each cinema or home then works out which of its own speakers should play the sound. So the same mix works in a cinema with 60 speakers, in a living room with a soundbar, and in a pair of headphones.
Consider a sound mixer in Chennai working on a Tamil action film. In one scene, a helicopter passes over a crowd. The mixer places the helicopter's sound as an object that starts behind the audience, rises overhead and moves to the front of the screen. In a cinema, the sound plays from the ceiling speakers. At home, a soundbar sends it upwards so that it bounces off the ceiling. On a phone with headphones, the software changes the sound so that it seems to come from above.
HDR works on the same idea for the picture. Brightness is measured in nits. An ordinary TV picture is graded for a peak of about 100 nits. An HDR picture can be graded for 1,000 nits or more, so a flash of sunlight on water looks bright, while a dark room still shows detail. HDR also needs more shades of each colour, so it uses 10 or 12 bits for each colour instead of 8. Some HDR formats store extra information for each scene, called metadata. It tells each TV how to fit the picture to its own brightness. A TV that reaches only 500 nits uses it to show the scene as well as it can.
The film is mastered in these formats after the visual effects, colour and sound work is finished. The format owners also make the codecs and tools with which these masters are compressed. The cinema version is played by a digital cinema server. The home version is compressed by video encoding software and sent by a streaming service. On a smart TV, the TV's operating system must support the format, or the TV plays an ordinary version instead.