This revised Rec. ITU-T H.264 adds the interface to support eleven new SEI messages, namely 1) SEI processing order, 2) processing order nesting, 3) encoder optimization information, 4) source picture timing information, 5) modality information, 6) digitally signed content initialization, 7) digitally signed content selection, 8) digitally signed content verification, 9) generative face video, 10) generative enhancement face video, and 11) AI usage restrictions request, through referencing the Versatile Supplemental Enhancement Information (VSEI) standard (Rec. ITU T H.274 | ISO/IEC 23002‑7), including a new mechanism that allows future extensions of the newly introduced SEI messages. It also adds support to interface extended versions of the film grain characteristics and neural network post-filter activation SEI messages through referencing the VSEI standard. The changes in this edition also include corrections to various minor defects in the prior content of the Recommendation. This Recommendation was developed jointly with ISO/IEC JTC 1, Information technology, Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information, and Rec. ITU-T H.264 is maintained as technically aligned twin text with ISO/IEC 14496-10. This version corresponds to a not-yet-published edition of ISO/IEC 14496-10 that is in preparation for publication.