1、 NASA STD-2821 Approval Date: 02/08/12 Expiration Date: None Audio and Video Standards for Internet Resources Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 2 of 17 FOREWORD The evolution of audio and video resources on the World W
2、ide Web has grown beyond a fashionable trend and is fast becoming a primary means for communicating to a global audience. However, a result of this increasing success has led to such a wide range of competing codecs, media players, formats, wrappers, viewing devices and delivery options that accessi
3、ng content has become increasingly confusing and can discourage even the most savvy web users. The National Aeronautic and Space Administration (NASA), a distinguished world class leader in Science, Engineering and Exploration has offered audio and video resources content on the internet for over a
4、decade, though these offerings have suffered because of rapid growth of these various options and formats. Due to this perplexity, it has become a priority of the agency to establish an audio and video resources standard for use by the entire Agency to assure that every effort is made to reach the g
5、reatest possible audience with the simplest means available. This standard has been developed by the NASA Web Video Working Group and is approved and published by NASA for use by NASA Headquarters, NASA Centers and their subsidiary locations as well as NASA contractors where applicable to NASA contr
6、actual agreements. This standard provides a comprehensive guide for all audio and video resources produced by or for the agency, and also defines applicable requirements for accessibility as required by Federal law. Requests for information, corrections, or additions to this standard should be submi
7、tted via “Feedback” in the NASA Technical Standards System at http:/standards.nasa.gov . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 3 of 17 TABLE OF CONTENTS 1. Scope 4 1.1 Purpose . 4 1.2 Applicability . 4 2. Applicable and Re
8、ference Documents 5 2.1 Applicable and Reference Documents 5 3. Acronyms and Definitions 7 3.1 Acronyms 7 3.2 Definitions . 7 4. Audio 11 4.1 MP3 Codec Usage . 11 4.2 AAC Codec Usage 11 5. Video 12 6. Content Delivery . 12 6.1 Download and Progressive Download 12 6.2 On Demand . 13 6.3 Live Streamin
9、g . 13 6.4 Recommended Encoding Specifications . 13 7. Accessibility 15 7.1 Captioning . 15 7.2 Audio Description 15 7.3 NASA Video on Third-Party Sites and Social Media Channels 15 7.4 Breaking News Exception 15 APPENDIX: HTML5 and Adobe Flash elements . 16 A.1 HTML5 . 16 Provided by IHSNot for Res
10、aleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 4 of 17 Audio and Video Standards for Internet Resources 1. Scope 1.1 Purpose This standard establishes requirements and responsibilities related to NASA audio and video resources for Internet Protocol delivery
11、. It contains requirements for audio and video codecs, bitrates and accessibility. 1.2 Applicability 1.2.1 Compliance with this standard is mandatory for all newly published NASA audio and video resources for Internet Protocol delivery, both internal and external. The individual NASA Centers are res
12、ponsible for implementation and enforcement. 1.2.2 This NASA standard is applicable to all audio and video content created for use on NASA controlled websites. 1.2.3 Any decision to waive or vary from the requirements in this NASA-STD requires the concurrence of the NASA Web Video Working Group, Con
13、figuration Control Board. 1.2.4 Within this NASA standard, the word “shall” indicates a mandatory requirement, the word “should” indicates that a statement is strongly recommended for implementation but not required, and the word “may” indicates an optional implementation. 1.3 General Guidance 1.3.1
14、 This document establishes at minimum, the necessary parameters for internet audio and video delivery and is intended to be the foundation for content delivered through current industry practices. Further consideration shall be given to include appropriate metadata as appropriate for the specific me
15、dia type, or at minimum, compliant with the Dublin Core Metadata Element Set. Due to the constant evolution of internet technologies these requirements are subject to change. These requirements shall apply to all NASA audio and video produced for the internet. All NASA Centers and facilities are res
16、ponsible for keeping up to date with applicable Federal accessibility requirements. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 5 of 17 2. Applicable and Reference Documents 2.1 Applicable and Reference Documents The documents l
17、isted in this section are accessible via the World Wide Web, or directly from the Standards Developing Organizations (SDO) or other document distributors. Federal Regulations: Rehabilitation Act of 1973 (29 U.S.C. 794d) as amended by the Workforce Investment Act of 1998 (P.L. 105 - 220), August 7, 1
18、998. http:/www.section508.gov/index.cfm?fuseAction=1998Amend o - 1194.22 Web-based intranet and internet information and applications. http:/access-board.gov/sec508/guide/1194.22.htm o - 1194.24 Video and audio and video resources products. http:/access-board.gov/sec508/guide/1194.24.htm U.S. Depart
19、ment of Health and Human Services o http:/www.hhs.gov/web/policies/videocaptionguidance.html NASA Publications: Electronic and Information Technology Accessibility o NASA Procedural Requirements NPR:2800.2 http:/nodis3.gsfc.nasa.gov/npg_img/N_PR_2800_0002_/N_PR_2800_0002_.pdf o Section 508 and Web V
20、ideo White Paper https:/share.nasa.gov/teams/msfc/dvwg/wvwg/Shared Documents/Section 508 and Web Video.docx Reference Documents: W3C HTML5 o http:/dev.w3.org/html5/spec/Overview.html Dublin Core Metadata Element Set (ISO Standard 15836:2009) o http:/dublincore.org/documents/2010/10/11/dces/ VMIX Vid
21、eo Upload Guidelines o http:/ software and hardware. A software codec is a computer application that utilizes algorithms to either compress or decompress digital audio data according to a specific audio or streaming format. Compressing audio data reduces the bandwidth necessary to deliver the data o
22、ver the internet and retain as much of the original file clarity as possible. A hardware codec is a device that converts analog audio into digital data or subsequently can convert a digital audio file to an analog format. Audio Description: An additional narration track added to a videos soundtrack
23、that vocally describes what is being seen in the video. Its intension is to aid visually impaired individuals when accessing video content. Bitrate: Audio and video resources bitrate refers to the number of bits encoded/decoded per second necessary to produce/reproduce a continuous audio or video ex
24、perience. Codec: a device or software that enables compression and/or decompression of digital media Closed Captioning: Allows individuals with hearing disabilities to access visual media by displaying the audio portion of a program textually on the screen. Closed Captioning can be turned on or off
25、by the end user and is required by law to be included in all federally produced audio and video resources content. Flash Media: Usually referred to simply as “Flash“ this is a proprietary video format developed by Adobe Systems Inc. for encoding and delivery of audio and video resources over the int
26、ernet. Frame Size: Width and height of a frame measured in pixels. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 8 of 17 Format: A particular way that information is encoded for storage in a computer file. H.264: H.264/MPEG-4 Part
27、 10 or AVC (Advanced Video Coding) is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video. The final drafting work on the first version of the standard was completed in May 2003. HTML5: The
28、 next major revision of HTML (Hypertext Markup Language) currently under development by the Web Hypertext Application Technology Working Group (WHATWG) and the World Wide Web Consortium (W3C). It is a language for structuring and presenting content for the World Wide Web, a core technology of the In
29、ternet. Its core aims have been to improve the language with support for the latest audio and video resources while keeping it easily readable by humans and consistently understood by computers and devices (web browsers, parsers etc.). International Electrotechnical Commission: The IEC is a non-prof
30、it, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies collectively known as “electrotechnology“. The IEC charter embraces all electrotechnologies including energy production and distributi
31、on, electronics, magnetics and electromagnetics, electroacoustics, audio and video resources and telecommunication, as well as associated general disciplines such as terminology and symbols, electromagnetic compatibility (by its Advisory Committee on Electromagnetic Compatibility, ACEC), measurement
32、 and performance, dependability, design and development, safety and the environment. Letterboxing: The practice of transferring film shot in a widescreen aspect ratio to standard-width video formats while preserving the films original aspect ratio. The resulting videographic image has mattes (black
33、bars) above and below it; these mattes are part of the image (i.e., of each frame of the video signal). Live Webcast: A media file distributed live (rather than “on demand”) over the Internet using streaming media technology to distribute a single content source to many simultaneous listeners/viewer
34、s Lossy compression: A data encoding method which compresses data by discarding (losing) some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer. Metadata: Metadata simply means “data about data“. Metadata articulates a context fo
35、r objects of interest. The modern “metadata“ field that gave rise to Dublin Core and other recent standards emerged with the Web revolution of the mid-1990s. Metadata is particularly useful in video, where information about its contents is not directly understandable by a computer. MP3: MP3 is an au
36、dio-specific format that was designed by the Moving Picture Experts Group as part of its MPEG-1 standard and later extended in MPEG-2 standard. MPEG: Refers to the Moving Picture Experts Group, a working group of experts that was formed by ISO and IEC to set standards for audio and video compression
37、 and transmission. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 9 of 17 MIME type: An Internet media type, originally called a MIME type after MIME (Multipurpose Internet Mail Extensions) used as a standard way of exchanging info
38、rmation over the Internet. Many e-mail clients now support MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. Audio and video resources: Media and content that uses a combination of different content forms On-demand Webcast: Often synonymous w
39、ith Video on Demand (VOD) that allows a viewer to watch a webcast anytime they want on their own schedule. Pillarboxing: Occurs in widescreen video displays when black bars (mattes or masking) are placed on the sides of the image. It becomes necessary when film or video that was not originally desig
40、ned for widescreen is shown on a widescreen display, or a narrower widescreen image is displayed within a wider aspect ratio, such as a 1.85:1 image in a 2.35:1 frame. The original material is shrunk and placed in the middle of the widescreen frame. Podcast: A non-streamed webcast which broadcasts a
41、 series of digital media files (either audio or video) that are released episodically and often downloaded through web syndication. The word replaced webcast in common vernacular due to the fame of the iPod and its role in the rising popularity and innovation of web feeds. Progressive Download: The
42、transfer of digital media files from a server to a client, typically using the HTTP protocol when initiated from a computer. The consumer may begin playback of the media before the download is complete. A media player that is capable of progressive download playback relies on metadata located in the
43、 header of the file to be intact and a local buffer of the digital media file as it is downloaded from a web server. At the point in which a specified amount of data becomes available to the local playback device, the media will begin to play. This specified amount of buffer is embedded into the fil
44、e by the producer of the content in the encoder settings and is reinforced by additional buffer settings imposed by the media player. Streaming Video: Video that is constantly received by and presented to an end-user while being delivered by a streaming provider. The name refers to the delivery meth
45、od of the medium rather than to the medium itself. The distinction is usually applied to video that is distributed over telecommunications networks, as most other delivery systems are either inherently streaming (e.g., radio, television) or inherently non-streaming (e.g., books, video cassettes, aud
46、io CDs). The verb to stream is also derived from this term, meaning to deliver media in this manner. Internet television is a commonly streamed medium. Video codec: There are two schemas for video codecs; software and hardware. A software codec is a computer application that utilizes algorithms to e
47、ither compress or decompress digital video data according to a specific video or streaming format. Compressing video data reduces the bandwidth necessary to deliver the data over the Internet and maintain the clarity of the original file as much as possible. A hardware codec is a device that convert
48、s analog video into digital data or subsequently can convert a digital video file to an analog format. VOD: Video On Demand (see On Demand Webcast) Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA STD-XXX Page 10 of 17 W3C: The World Wide Web Con
49、sortium (W3C) is an international community that develops standards to ensure the long-term growth of the Web. Windowboxing: The effect seen as a black border all around the video image. It occurs when the aspect ratio of the media is such that the in the display of film or video occurs letterbox effect and pillarbox effect occur s
