An Extensive Guide to Closed Captions and Subtitle File Formats

Subtitles are used all over the world to help make video content more accessible. To viewers, the concept behind subtitling is a very simple thing. In this blog, we will go through an extensive guide to closed captions and subtitle file formats and we’ll consider why they are different, when each is required, and what are the consequences if the wrong type of captions are used.

Subtitles and closed captions simply consist of onscreen text that displays to convey dialogue and/or sound effects as required by foreign speakers or viewers who are deaf or hard of hearing. Only when you are producing content either for broadcast, a live audience or online, does it become apparent how many different options there are when it comes to captioning services.

Standard Online Subtitles

For basic online, dialogue only subtitles, SRT is the go-to format. It’s the simplest to create, the easiest to edit and the most widely compatible for use with online video. There are two scenarios in which SRT subtitling is likely to be your best option:

• SRT for Social Media and Websites

SRT subtitles are a simple format, great for videomakers new to subtitling  who want to upload a caption file in the simplest way possible, for subtitling on social media sites such as YouTube, Vimeo or Facebook.

• SRT for Easy Editing

Experienced video producers who want to have greater control over their subtitles often use SRT files during editing. The simplicity of the format means you can alter timings and the look of your subtitles as you go. SRT is also a recommended format if the subtitles need to be imported into software such as Premiere or Final Cut and then embedded/burned into the video.

Broadcast Closed Captions

Closed captions created for broadcast purposes will have a requirement to include descriptions for the Deaf and Hard of Hearing. Depending on the channel where the show or film will be distributed, there will be specifications around what should be included, and the style in which the subtitles should be displayed. Reading speeds may also be defined, with slower speeds for children’s subtitles and faster speeds allowed for adult shows. Some of the most commonly requested broadcast formats are outlined below.

• CAP and SCC captions

Though fast becoming a legacy software, many distributors still request SCC closed captions for broadcast content. This is a closed caption format with strict 32 character limits. There are also limitations on characters used and some language limitations.

• STL captions

With greater flexibility on characters, with 42 character limits, STL open captions are often requested alongside SCC captions. Reading speeds will be specified by the distributor, as will writing styles and requests for italics and other specific formatting. Similar to SCC, the STL caption format does have some limitations in terms of supported characters.

• TTML, DFXP and EBU-TT Captions

All displaying as XML format captions, these formats aim to replace the legacy SCC format over time. The TTML format has much greater compatibility. For EBU-TT, character limits should be set to 37. For TTML and DFXP, there is greater flexibility on this.

SDH (Subtitles for Deaf and Hard of Hearing)

Closed captions created for deaf and hard of hearing viewers should have a number of elements to ensure they are fit for purpose. They can be listed as below:

• Caption descriptions of sound effects.

These are typically described within square or round brackets, sitting as standalone captions. They can describe music or noises relevant to the context of the video.

• Voice descriptions.

Voice descriptions can be used to describe the tone of a speaker, where intonation may not be read properly through text. For instance, a tone of sarcasm, shouting, whispering, or using a silly voice or accent.

• Use of italics.

Italics are normally used within closed captions to indicate a speaker is offscreen or to show narration over a video. This helps to avoid any confusion on speakers who are not present within a scene.

• Colours and/or caption placements.

Foreign Subtitles

Subtitles created for translation purposes for foreign audiences should typically only include dialogue and not descriptions for the Deaf and Hard of Hearing. Specific fonts may need to be used for certain languages and some caption formats may not be compatible for certain languages. In terms of SCC captions, 708 closed captions offer more flexibility and support for international characters. Below are some typical scenarios for the use of foreign subtitling.

• Subtitle translation

Subtitltle translation is often requested for feature films and documentaries in broadcast formats. In these cases, only dialogue will be subtitled, and elements for the Deaf and Hard of Hearing will be removed.

• Foreign subtitles

Foreign subtitles are often burned into films which may be displayed at festivals or events where the audience speaks a different language to the source video.

Forced Narrative Subtitles

Forced narrative subtitles are used to translate content that is in a foreign language within a film, where that language is not dominantly used throughout. For example, an English film with short sections of Chinese speakers should have subtitles that will appear for all viewers only when Chinese is spoken. These subtitles are often burned in but in cases where closed captions will be used and/or other foreign subtitles, they are required to be flagged as forced narrative, meaning those captions are ‘forced’ onto the screen whether subtitles are turned on or off.

Forced narrative subtitles are also used for onscreen text and/or titles for foreign audiences. A subtitle file will contain dialogue only in the source language, for a translator to work from. However, onscreen text would be in the source language so would then also require translation, so should be included within forced narrative.

Forced narratives should be flagged within a caption file and often, broadcasters will request the below:

• A caption file which includes both all caption text and forced narratives, appropriately flagged.
• A caption file including caption text (dialogue and sound effects only) with forced narrative removed.
• A caption file which contains only forced narrative.

DLP / DCP Closed Captions and XML (Digital Cinema Package)

Used for cinema releases and festivals, closed captions will be supplied in a Digital Light Processing format. This format can be imported and used within a DCP, where cinema projectors and servers can display them properly. An XML exported as a DLP should have three files – one containing the captions, another containing ID and metadata information, and a final file containing the font. DLP files are timed text and can be exported as SMPTE, which is an industry standard frame based format used as standard. They can also be exported as DTS-CSS, which uses a DTS timecode and is the standard for cinema.

So there you have it, whether it’s online subtitles, Digital Cinema Packages, subtitle translations and broadcast Captions – we’ve got them covered! So as you can see from this extensive guide to closed captions and subtitle file formats, using the correct format from the start will save you a lot of time and money when it comes to getting your subtitles correct. 

An extensive guide to closed captions and subtitle file formats should give you all the information you need to know. If you would like to know more about these services or any other services we currently offer then visit our website today or click the button below to get your quote today.