The diversity of devices in both wired and wireless networks via which multimedia contents are desired to be accessed and interacted with has grown significantly. Applications like video conferencing, surveillance and chatting is challenged by this diversity which requires live adaptation to meet user requirements and device specifications. In this paper, we present an architecture for temporal adaptation of ITU-T H.264 video conforming to ISO/IEC MPEG-21 DIA for live video stream along with the adaptation module implementation detail. Adaptation is performed on demand directly from the live bitstream and its generic Bitstream Syntax Description (gBSD) avoiding conventional approaches seen in traditional transcoders. As a result, any MPEG-21 compliant host can adapt the stream without requiring the video codec. A prototype, based on the proposed architecture, and experimental evaluations of the system and its performance supporting the architecture are also presented.