Main 10 is the HEVC profile that supports 10-bit colour at 4:2:0 chroma subsampling. The plain Main profile of HEVC supports only 8-bit; Main 10 adds the extra bit depth while keeping everything else (same coding tools, same hardware decoders) — and it's the profile that all HDR HEVC content uses, because HDR cannot exist in 8-bit without producing ugly banding.
The history is unusual. When HEVC was being standardised, most engineers assumed Main (8-bit) would be the universal profile and Main 10 a niche for production. The opposite happened: as HDR moved from concept to mainstream, every streaming service mastering 4K HDR (Netflix, Amazon, Disney+, Apple TV+) standardised on Main 10. Hardware decoder vendors (Apple, NVIDIA, Intel, AMD, smart TV chipset makers) responded by making Main 10 hardware decode universal on devices from ~2017 onwards. Today, Main is essentially gone outside legacy contexts; Main 10 is the modern HEVC.
For a product team, the practical rule is: if you're encoding HEVC for delivery in 2026, use Main 10 by default. It works on every modern device, gives the extra bit depth even on SDR content (where it slightly improves compression efficiency at zero perceptual cost), and is the only profile that supports HDR. There's also Main 4:2:2 10, Main 4:4:4 10 and so on for production scenarios, but for streaming delivery Main 10 + 4:2:0 + BT.709 (for SDR) or Main 10 + 4:2:0 + BT.2020 + PQ (for HDR) is the universal recipe.
