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What Is Closed Captioning?

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    Closed captions are chunks of time-synchronized text that reflect the audio track and can be read while watching the video. The process of closed captioning involves transcribing the audio to text, dividing the text into chunks known as “caption frames,” and then synchronizing the caption frames with the video. Closed captions are typically located underneath the video or overlaid on top of the video.

    Captions should assume that the viewer cannot hear the audio at all. Closed captions should convey not only the spoken content, but also any sound effects, speaker identification, and other non-speech elements. In this way, captions are different from subtitles, which assume that the viewer can hear but cannot understand the language. Learn more about the difference between closed captions, subtitles, and SDH (subtitles for the deaf and hard of hearing).

    Closed captions should account for any sound that is not visually apparent but is integral to the plot. For example, the sound of keys jangling should be included in closed captions if it is important to the plot development–like in the case where a person is standing behind a locked door. However, it should not be included if it is the sound of keys jangling in someone’s pocket while they are walking down the street. Learn more about captioning and subtitling standards.

    Origin of Closed Captions

    Closed captions originated in the early 1980s as a result of an FCC mandate and gradually became a requirement for most programming on broadcast television. Accessibility laws went on to require closed captions for Internet video, and have become available across many different types of devices and media. The original purpose of closed captions was to provide accommodations for people with hearing disabilities. However, it turns out that most people who use closed captions are not deaf or hard of hearing. Closed captions are often used because they improve comprehension and remove language barriers, especially for people who know English as a second language. Closed captions also compensate for poor audio quality or a noisy background, and allow the video to be consumed in sound sensitive environments like a workplace.

    What Are Closed Captions?

    Closed Captioning Terminology

    Captions vs. Transcript

    The difference between captions and a transcript is that a transcript is not synchronized with the media. Transcripts are sufficient for audio-only content like a podcast, but captions are required for videos or presentations with a voice-over.

    Closed Captions vs. Open Captions

    The difference between closed and open captions is that closed captions allow the viewer to turn the captions on and off. Open captions are burned into the video and cannot be turned off. Closed captions are more common with online video. See a demo of open vs. closed captions.

    Post-Production vs. Live Captions

    Post-production captions (aka “offline captions”) versus live captions (aka “real-time captions”) refers to the timing of when the captioning process is done. Live captioning is done in real time by stenographers while the event is happening. Post-production captioning is done after the event has taken place.

    Closed Captions vs. Subtitles vs. SDH

    In the US, “closed captions” are designed for viewers who are deaf and hard of hearing. In addition to the spoken words, closed captions convey sound effects, speaker identification, and other non-speech elements. On the other hand, “subtitles” are intended for viewers who can hear the audio, but cannot understand the language. For this reason, American subtitles communicate the spoken content but not the sound effects. Outside of the U.S., the words “subtitles” and “closed captions” are often used interchangeably. “SDH” means “subtitles for the deaf and hard-of-hearing.” SDH subtitles convey the same information as closed captions but in some cases have technical differences. For more information, read the article How Subtitles for the Deaf and Hard-of-Hearing (SDH) Differ from Closed Captions

    Closed Caption Formats

    There are many different caption formats that are used depending on the type of media player or device. Below is a list of some of the more common caption formats and their respective applications.

    Format Type Use Cases
    SCC Broadcast, iOS, web media
    SMPTE-TT Web media
    CAP Broadcast
    EBU.STL PAL Broadcast
    DFXP Flash players
    SRT YouTube and web media
    WebVTT HTML5
    SAMI Microsoft / Windows Media
    QT QuickText / QuickTime
    STL DVD encoding
    CPT.XML Captionate
    RT Real Media

    Examples of SCC and SRT caption formats

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