H．264可分级扩展是ISO／IEC组织和国际电信联盟最新的联合标准制订工作。目前，H．264扩展标准仍处于制订过程中，但其主体框架已基本确定。为了使人们对正在制定的H．264扩展标准有一概略了解。该文首先对扩展标准的主体框架作了简要介绍，并阐述了实现空域、时域和质量可分级的机制，然后对其中的层间编码和精细质量可分级编码包含的关键技术进行了较为详细的分析，并利用最新的参考软件JSVM5．7进行了性能以及复杂度的比较和测试，结果表明，该项技术在具有良好的支持分级能力的同时，可保持较高的编码效率。

The scalable extension of H. 264 is the newest work of developing joint standards for ISO/IEC and ITU. Now, this project is still in progress, and yet the main frame of the extension standard has been established. In order to make the ongoing standard known to people, in this paper a short introduction about the main frame of the H. 264 extension standard is provided first, with the mechanism of implementing spatial, temporal and quality scalability explained. Then the key techniques involved in inter-layer coding and fine grain quality scalable coding are analyzed in detail. Making use of the newest reference software JSVM5. 7, we carry out some comparisons and tests on performance and complexity, which verify that those techniques keep quite good coding efficiency together with satisfactory scalable performance.