流媒体的封闭字幕

Though relatively few websites are required to provide closed captions for their videos, any website with significant video content should consider captioning. Not only does it provide access for deaf and hard-of-hearing viewers, but captions and the associated metadata can dramatically improve video search engine optimization. 在这个介绍中，要加上封闭的字幕, you’ll learn about who needs to caption and who doesn’t (and why you may want to anyway), the available workflows for captioning live events and 随需应变 files, and a bit about web caption formats and how to marry them to your streaming files.

让我们开始吧.

什么是封闭字幕?

Closed captions enable deaf and hard-of-hearing individuals to access the audio components of the audio/video experience. Closed captions incorporate all elements of the audio experience, 包括识别背景声音, 说话人的身份, 背景音乐的存在, 对说话人说话方式的描述, 类似的信息. They are also closed, so they can be disabled for viewers with no hearing disabilities. In contrast, open captions are burned into the video stream and can’t be disabled.

Subtitles are typically implemented to allow viewers to watch videos produced in different languages. 从技术上讲, background sounds and other nonvocal audio don’t have to be incorporated into the text description, since subtitles are not designed for the deaf and hard-of-hearing, 但这些元素通常都包含在内. There are many closed captions standards, and several are discussed here. 虽然每个都有独特的格式和结构, 所有闭标题文件的内容都是相似的, primarily consisting of the textual data and time code 信息 that dictates when it’s displayed.

谁必须使用封闭字幕?

Two classes of websites caption; those required by law and those who caption voluntarily. 让我们从法律要求的标题开始.

康复法案第508条

四项法律规定了标题的义务. 从联邦机构开始，第508 - 1194节.《百家乐软件app最新版下载》第24(c)条.S.C. 794d) states that “All training and 信息al video and multimedia productions which support the agency’s mission, 不管格式如何, that contain speech or other audio 信息 necessary for the comprehension of the content, 应为开式或闭式字幕.“超出了这些联邦要求, note that states that receive federal funds under the Assistive Technology Act of 1998 must also comply with Section 508 to some degree.

Interestingly, several agencies meet this requirement via YouTube’s captioning. 例如, the surgeon general videos available from the Department of Health and Human Services website use YouTube (图1)，美国国税局(IRS)的视频也是如此.gov和我的家乡弗吉尼亚州. 更多关于如何使用YouTube的内容如下.

图1. Videos from the Department of Health and Human Services website use YouTube’s captioning system to meet the Section 508 requirements.

Twenty-First Century Communications and Video Accessibility Act of 2010

The next class of producers who must add closed captions to their streaming videos are broadcasters, but only with regard to content that has been previously played on TV with closed captions. 具体地说, under powers flowing from the Twenty-First Century Communications and Video Accessibility Act of 2010, the Federal Communications Commission issued regulations called the IP Closed Captioning rules in August 2012, which went into effect for some classes of video soon thereafter on Sept. 30, 2012.

这是, prerecorded programming that was not edited for internet distribution must be captioned for the web if it was shown on television on or after Sept. 30, 2012. If content was edited for internet distribution, the deadline is pushed back a year until Sept. 30, 2013. 还包括其他几类内容, including live content published with captions on TV, which must be captioned on the internet by March 30, 2013, 以及早于该法案的旧内容.

The FCC regulations and interpretations thereof make several points clear. If the content is never shown on television with captions, 流媒体不需要字幕. The rules also only relate to full-length programming, not clips or highlights of this programming. This last point explained why ESPN’s full-length shows such as Mike & 早上的迈克(图2) do have captioning, while none of the highlights that I watched do.

图2. ESPN captions programs that displayed in their entirety on TV.

有关条例的更多资料, check out “FCC’s New Closed Captioning Rules Kick Into Gear” on the FCC法律博客.

其他不公开字幕规定

Several additional federal laws may impose captioning requirements on varying classes of publisher. 例如, some authorities opine that Title II of the Americans with Disabilities Act (“Title II”) and Section 504 of the Rehabilitation Act of 1973 (“Section 504”) imposed captioning requirements on public schools, 公立大学, 以及城镇和其他市政机构. 这里有相互矛盾的观点, 虽然, and I bring it up not to take a position either way but to advise that the obligation may exist. Don’t contact me; contact your attorney.

Wowza Media Server 3中的封闭字幕.5

The introduction of caption transmuxing simplifies deployment by minimizing the number of source files required, 虽然 the process is slightly different for live vs. 随需应变

2012年11月27日