Best Practices for Closed Captioning IP Video Programming
Updated: June 3, 2019
Earlier this year, 3Play Media co-sponsored the Entertainment Merchants Association (EMA) Closed Captioning Conference. The EMA Closed Captions Working Group is comprised of North America’s most prominent names in home entertainment, including Netflix, Amazon, Google, Microsoft, and Best Buy. This group’s work has proposed standards for video accessibility that EMA members can reference to stay compliant with federal regulations. The group is particularly interested in how to convert television closed caption files to closed captioning for Internet protocol (IP) delivered video programming. Recently, the group released the document EMA’s Best Practices for Closed Captioning of Internet Protocol‐Delivered Video Programming. This blog post summarizes this document to provide the technical requirements of closed captioning IP video programming and EMA recommendations for converting TV closed captions for Internet streaming.
Standard for Closed Captioning of IP Video Programming
The Federal Communications Commission requires that all full-length videos delivered via Internet protocol (IP) have closed captions if they air on broadcast or cable television with closed captions. As such, the EMA Closed Captions Working Group was created to better understand the legal requirements for closed captioning of IP video programing. Captioning requirements have been dependent on various deadlines for online video accessibility, directed by the 21st Century Video Accessibility Act (CVAA) and enforced by the FCC.
The content licensor or “video programming owner” (VPO) is to supply a closed captioning file to the online video service, sometimes called the “video programming distributor” (VPD) or “video programming provider” (VPP). Both of these parties are to establish a mechanism for ongoing communication as to whether a particular video is covered by the closed captioning requirement or not. Furthermore, the online video service must make a good faith effort to identify covered programming using that mechanism
When a Closed Caption File is Not Available
Sometimes a closed caption file is not provided for a piece of IP‐delivered video programming. Occasionally this is to be expected. The VPO should include one of the below statements in both the avails and the metadata for that programming:
- This content has never aired on television in the U.S.
- This content has only aired on television in the U.S. without captions.
- This content has not aired on U.S. television with captions since September 30, 2012.
- This content does not consist of full‐length video programming.
- This content does not fall within a category of online programming that currently requires captions under FCC regulations.
- The FCC and/or U.S. Congress has granted an exemption from captioning requirements for this content.
More about the EMA
Established in 2006, the Entertainment Merchants Association (EMA) is a not-for-profit international trade association dedicated to advancing the interests of the home entertainment industry. EMA member companies sell and/or rent DVDs, computer/console video games and digitally distributed versions of these products. Members include retailers, distributors, video game publishers and home video divisions of major and independent motion picture studios as well as related businesses.
Preferred Caption Formats
For a broadcast video to be delivered via the Internet with closed captions, the closed caption file must be converted from the CEA‐608 protocol used for television to a format suitable for Internet delivery. Captions can then be edited to display properly online. There are several file formats suitable for Internet delivery: SCC, SMPTE-TT and DFXP. Conversion from CEA-608 and subsequent editing can be done manually or from scratch. These options are undesirable because they are time-consuming and expensive. The EMA Closed Captions Working Group suggests utilizing software to extract and reformat the captioning data. With closed captioning software, conversion can be challenging, especially when it involves a broadcast closed caption file in a legacy format. It is best to have the closed caption file delivered in a format that is relatively easy to extract and reformat.
Best Practices for the Conversion of Television Closed Captions
The preferred file format for delivery of closed caption files at this time is the SCC format (.scc file extension). The EMA working group favors the SCC format because it contains all of the CEA‐608 information and is very concise and unambiguous. It is also widely used and well understood by all captioning software. The working group proposed that the following TTML formats are also acceptable:
- SMPTE‐TT recommended practice 2052 (.xml file extension)
- DFXP Full/Timed Text Markup Language (.dfxp file extension)
Some additional notes and recommendations:
- Using TTML markup carries some risk of inoperability, even with recommended practice 2052. Suggest only using pop‐on captions (regions pop1‐4) to help simplify matters.
- Using the mechanism described in 5.10 of The Conversion of CEA-608 Data to SMPTE-TT to tunnel CEA‐608 data results in unambiguous behavior.
- Using arbitrary TTML as defined by WC3 Timed Text Markup Language recommendations without reference to recommended practice 2052 is strongly discouraged.
- Other formats are not preferred because they are proprietary, not open source or cause technical issues.
Suggested Process for Caption Frame Rates
The EMA working group also proposed some best practices to address caption frame rate issues. Closed caption data files are separate from the video data files. Ideally, the caption frame rate should match the native frame rate of the source. However, synchronization of the two can be a problem. Why is this? Television in North America is usually broadcast at a rate of 29.97 frames per second (FPS). Internet video delivery, however, can support a variety of frame rate formats and a number of VPDs require films and TV shows stream at a frame rate of 23.976 or 25 FPS. This means that frame rate requirements for North American broadcast TV will not match requirements for the Internet video frame rate. As a result, the frame rate of the caption file must be reconfigured to the frame rate utilized by the Internet video content distributor, and if necessary, the time code must be stretched or shrunk. This is easier said than done. Potential frame rate difficulties include:
- The caption file has SMPTE based timestamps and fails to specify the frame rate.
- The video has been transcoded to a slightly different frame rate, or the captions were generated using a differently transcoded or edited version of the video.
To address this problem some Internet video content distributors require the VPO to provide a closed caption data file whose frame rate is already synchronized with the video data file. Other content distributors fix the caption files in‐house.
Have more questions about closed captioning IP video programming? Don’t hesitate to get in touch with 3Play Media
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