Profile names in H.264

Posted Mar 27, 2025 9:34 UTC (Thu) by farnz (subscriber, #17727)
In reply to: The world beyond OpenH264 by numgmt
Parent article: Bhattcharya: Closing the chapter on OpenH264

Confusingly, High Profile and High 10 Profile are separate profiles. You can fully support High Profile, and have no support for High 10 Profile; the difference between High Profile and High 10 Profile is simply that High Profile only supports 8 bpc, while High 10 Profile supports 8, 9 and 10 bpc.

And remember that the decoder's behaviour is fully specified by the standard; a High 10 Profile bitstream can assume that if a 9 bpc picture is in the set of reference pictures, it's in there at 9 bpc, and thus pictures that reference the 9 bpc picture will be doing their differences against the 9 bpc reference, not that reference truncated to 8 bpc. And since H.264 allows for reference pictures to themselves be reconstructed from previous reference pictures, the error can accumulate quite quickly, going from "off by the LSB" to "reduced to 4 bpc of data plus 4 bpc of noise" if you use an 8 bpc truncated reference.