ISO/IEC TS 20071-21:2015提供了以听觉模式描述视听内容的建议，以用于录制视频演示、广播电视、电影、现场或录制的戏剧、博物馆和艺术画廊展览、遗产旅游、新闻和喜剧，而不考虑用于传输和呈现录制或现场视听内容的语言和技术。 注1:音频描述有许多次用户，但音频描述的主要和预期用户是盲人或视力低下者及其朋友和家人。 ISO/IEC TS 20071-21:2015对创建音频描述的主观性质提供了指导。 它还为音频描述开发者（脚本作者、声音叙述者以及负责提供音频描述的组织或团体）提供了忠实、准确地表示视听内容的指导。 注2:由于音频描述的可用时间有限，根据所描述的内容，可能并不总是能够提供同等的体验。 ISO/IEC TS 771-21:2015适用于描述视听内容，并且不考虑用于传递内容或音频描述的设备或传输机制。这些设备包括但不限于电视、计算机、无线设备、投影设备、DVD和家庭影院设备以及其他形式的用户界面技术。因此，ISO/IEC 20071的这一部分不考虑对各种视频输出的代码转换文件。 注3:传输和分配的技术问题由其他国际标准（如MPEG标准和其他技术国际标准，如IEC 62731）涵盖。 ISO/IEC TS 20071-21:2015提供了关于如何处理用户偏好、可用风格和音频描述方法灵活性的指南。 它不适用于电子文档中包含的静态图像（有关图像的文本替代指南，请参见ISO/IEC 20071-11）。 它适用于与原始视听内容同时传输或交付的听觉演示。 注4:广播公司或同步环境中的人员所经历的限制可能会在在线或异步环境中减少。

ISO/IEC TS 20071-21:2015 provides recommendations for describing audiovisual content in an auditory modality for use in recorded video presentations, broadcast television, cinema, live or recorded drama, museum and art gallery exhibits, heritage tours, news, and comedies, regardless of the language and technology being used to transmit and present the recorded or live audiovisual content. NOTE 1 There are many secondary users of audio description, but the primary and intended users of audio description are blind persons or persons with low vision and their friends and family. ISO/IEC TS 20071-21:2015 provides guidance on the subjective nature of creating audio description. It also provides guidance for audio description developers (script writers, voice narrators, and organizations or groups responsible for delivering audio description) in faithfully and accurately representing audiovisual content. NOTE 2 It might not always be possible to provide an equivalent experience due to limitations in the amount of time available for audio description depending on the content being described. ISO/IEC TS 20071-21:2015 applies to describing audiovisual content and does not consider the devices or transmission mechanisms used to deliver the content or the audio description. These devices include, but are not limited to, televisions, computers, wireless devices, projection equipment, DVD and home cinema equipment and other forms of user interface technology. Therefore, this part of ISO/IEC 20071 does not consider transcoding files for the various video outputs. NOTE 3 Technical matters of transmission and distribution are covered by other International Standards (e.g. MPEG standards and other technical international standards such as IEC 62731). ISO/IEC TS 20071-21:2015 provides guidance on how to approach user preferences, available styles and flexibility in approaches to audio description. It does not apply to static images contained in electronic documents (see ISO/IEC 20071？11 for guidance on text alternatives for images). It applies to auditory presentations intended to be transmitted or delivered simultaneously to the original audiovisual content. NOTE 4 Limitations experienced by broadcasters or people in synchronous environments might be reduced online or in asynchronous environments.