# Captions features supported in a channel This section provides information about the different features of captions that MediaLive supports. **Topics** + [ # Captions formats supported in a channel ](supported-formats.md) + [ # Formats supported in different types of outputs ](supported-format-outputs.md) + [ # Constraints for using OCR conversion ](captions-languages-ocr.md) + [ # Support for multiple captions languages ](support-for-languages.md) + [ # Support for font styles in output captions ](support-for-font-styles-in-output-captions.md) # Captions formats supported in a channel MediaLive supports specific formats in inputs and specific formats in outputs. See [General information about supported captions formats](general-information-supported-formats.md) for a table that lists the supported captions formats, with a reference to the standard that defines that format. The table specifies whether the format is supported as input or output or both. # Formats supported in different types of outputs There are several factors that control your ability to include captions of a specific format in the outputs in a MediaLive channel: + **The type of input container** – A given input container can contain captions in some formats and not in others. + **The format of the input captions** – A given format of captions can be converted to some formats and not to others. + **The type of output containers** – A given output container supports some captions formats and not others. For example, assume that your input container is an MP4 container and your output is HLS, and that you want to include WebVTT captions in the HLS output. You can implement this use case only if the MP4 container holds 608 embedded captions. You can't implement it if, for example, the MP4 container holds Ancillary captions. For more information about all the supported combinations of input container, input format, and output container, see [Captions supported in MediaLive](supported-captions.md). # Constraints for using OCR conversion MediaLive uses OCR (optical character recognition) technology for the following scenarios: + The input captions are DVB-Sub or SCTE-27 + The output captions are WebVTT format **Constraint in supported languages** OCR conversion uses language libraries. Language libraries are a critical component of conversion. They speed up conversion because the tool can check character strings against a dictionary, instead of recognizing words letter by letter. You must specify the language of a captions source so that MediaLive can choose the correct library. If you choose a language that doesn’t match the language of the captions, conversion accuracy will be poor. MediaLive currently includes libraries for six languages, which means that MediaLive can perform an OCR conversion only with the following source languages: + Dutch + English + French + German + Portuguese + Spanish **Constraint in number of languages in one input** OCR conversion uses more processing resources than other captions conversions. Therefore, in each input, you can create a maximum of three captions selectors that will use OCR conversion. These rules apply: + A selector uses OCR conversion if the specified format is DVB-Sub or SCTE-27, and at least one output encode that uses the selector is a [WebVTT encode](output-sidecar-and-smptett-mss.md). + A DVB-Sub or SCTE-27 selector doesn't use OCR conversion (and doesn't count towards the limit) if, for example, the selector is used only in SMPTE-TT encodes. + If the selector is used in more than one WebVTT encode (for example, in two output groups), the selector counts only once towards the limit. # Support for multiple captions languages Some captions sources that MediaLive supports typically include multiple languages. You can include multiple languages in the output as follows. | Source captions | Output captions | Result | | --- | --- | --- | | ARIB | ARIB (which is the only option for ARIB sources) | This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages. | | Embedded | Embedded | This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any of the languages. | | Embedded | Another format | You can specify which languages to extract and include in an output. | | DVB-Sub | Another format | If you have DVB-Sub source and want a different format in the output, you can specify the language to extract from the input and the language to include in an output. | | DVB-Sub | DVB-Sub | This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages. | | Teletext | Teletext | This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages.In fact, the entire Teletext content is included in the output; you can't remove out any of the pages. | | Teletext | Another format | You can specify the language to extract from the input and the language to include in an output. | | Any other combination | | For all other sources, you always specify the language to extract from the input and the language to include in an output, regardless of the source format and output format. | # Support for font styles in output captions Depending on the scenario, there are three possibilities for the font style for output captions in a MediaLive output. + You can specify the style that you want for fonts, including color, outline, and background color. + The font styles in the input are passed through. + The font styles are controlled by the downstream player. The procedures later in this chapter describe how to set up font styles. You might set up the styling of the output captions on the [input side](identify-captions-in-the-input.md), on the [output side](captions-outputs-details-specific-formats.md), or on both sides. | Source captions | Output captions | Options for font style | | --- | --- | --- | | ARIB | ARIB | None. The font styles in the input are automatically passed through in the output. | | Any supported captions format | Burn-in | You can specify font styles in the output. If you don’t specify styles, the AWS Elemental MediaLive defaults are used. | | DVB-Sub | DVB-Sub | None. The font styles in the input are automatically passed through in the output. | | Any supported captions format | DVB-Sub | You can specify font styles in the output. If you don’t specify styles, the AWS Elemental MediaLive defaults are used. | | An Embedded Combination (Embedded, Embedded\$1SCTE-20, SCTE-20\$1Embedded) | EBU-TT-D | You can specify some of the style information and take some of the information from the input captions. Or you can set up the captions with no style data. | | Teletext | EBU-TT-D | You can specify some of the style information and take some of the information from the input captions. Or you can set up the captions with no style data. | | Teletext | Teletext | None. The font styles in the input are automatically passed through in the output. | | An Embedded Combination (Embedded, Embedded\$1SCTE-20, SCTE-20\$1Embedded) | TTML | You can set up to copy the font information from the source to the output. Or you can let the downstream player determine the font style. | | Teletext | TTML | You can set up to copy the font information from the source to the output. Or you can let the downstream player determine the font style. | | An Embedded Combination (Embedded, Embedded\$1SCTE-20, SCTE-20\$1Embedded) | WebVTT | You can set up to pass through color and position style information from the source to the output. Or you can set up the captions with no style data. | | Teletext | WebVTT | You can set up to pass through color and position style information from the source to the output. Or you can set up the captions with no style data. | | Any Other | Any Other | No control: the font style is always determined by the downstream player. |