Create captions selectors in the inputs - MediaLive
Identify the captions that you wantCreate captions selectorsInformation for DVB-Sub or SCTE-27Information for embedded Information for Teletext

Create captions selectors in the inputs

This section describes the first step for setting up for captions in MediaLive. You must identify the captions that you want to use and assign each to a captions selector. If you don't create any captions selectors, you can't include captions in the output. All the captions will be removed from the media.

Then you must extract the captions that you want by adding a captions selector in the channel. Each extracted captions asset is contained in one captions selector. For example, one selector contains the Teletext captions in Czech.

Identify the captions that you want

  1. Identify which captions are in the input (the provider of the input should provide you with this information). Identify the captions formats and, for each format, the languages.

  2. Identify which of those formats and languages that you want to use.

  3. If you are converting DVB-Sub or SCTE-27 captions to WebVTT, there are limits on the number of languages that MediaLive can ingest. For more information, see Constraints for using OCR conversion.

  4. Determine how many captions selectors to create in the input in the channel. For guidance, see the table that appears after this procedure.

You end up with a list of captions selectors to create. For example:

  • Captions Selector 1: Teletext captions in Czech

  • Captions Selector 2: Teletext captions in Polish

Source captions Output captions Result
ARIB ARIB Create a single captions selector. All languages are passed through; there is no other option.
Embedded Embedded Create a single captions selector. All languages are passed through; there is no other option. For details, see Information for embedded .
Embedded Another format Specify the language to extract from the input and the language to include in an output. The specified language is extracted from the embedded captions and converted to the new format.
DVB-Sub WebVTT Create one caption selector for each language, to a maximum of three caption selectors in the input. For more information about this limit, see Constraints for using OCR conversion.
DVB-Sub SMPTE-TT Create one caption selector for each language. The specified language is extracted from the DVB-Sub captions and converted to the new format.
DVB-Sub DVB-Sub Create a single captions selector. All languages are passed through.
SCTE-27 WebVTT Create one caption selector for each language, to a maximum of three caption selectors in the input. For more information about this limit, see Constraints for using OCR conversion.
Teletext Teletext Create a single captions selector. All languages are passed through. All the pages in the teletext are passed through. For details, see Information for Teletext.
Teletext Another format If you have Teletext source and want a different format in the output, create one captions selector for each language and format combination.
Any other combination Create one captions selector for each language and format combination.

Create captions selectors

  1. In the channel that you are creating, in the navigation pane, in Input attachments, choose the input.

  2. Got to General input settings and choose Add captions selectors.

  3. In Captions selector name, enter a name that describes the captions in the source.. For example, Teletext Czech.

  4. In Selector settings, choose the format of the source captions.

  5. For most formats, more fields appear. For details about a field, choose the Info link next to the field. In addition, see DVB-Sub or SCTE-27, Embedded, or Teletext.

  6. Create more captions selectors, as required.

Information for DVB-Sub or SCTE-27

  1. You must specify the location of the captions.

    Complete the PID or Language code fields in one of the ways described in the following table. Each row in the table describes a valid way to complete these two fields.

    PID Language Code Result
    Specified Blank Extracts captions from the specified PID.
    Blank Specified Extracts the captions from the first PID that MediaLive encounters that matches the specified language. This might or might not be the PID with the lowest number.
    Specified Specified Extracts the captions from the specified PID. MediaLive ignores the language code, therefore we recommend you leave it blank.
    Blank Blank Valid only if the source is DVB-Sub and the output is DVB-Sub. With this combination of PID and Language, all input DVB-Sub PIDs are included in the output.

    Not valid for SCTE-27.

  2. If you plan to convert the captions to WebVTT, you must also specify the language of the captions.

    Complete the OCR language field to specify the language of the captions specified by this selector.

    MediaLive ignores any value in this field if you aren't converting the captions to WebVTT.

Information for embedded

Read this section if the input captions are any of the following: embedded (EIA-608 or CEA-708), embedded+SCTE-20, SCTE-20+embedded, or SCTE-20.

How many captions selectors?

  • Embedded passthrough – Create only one captions selector. With this scenario, all languages are automatically extracted and are automatically included in the output.

  • Embedded in, other out – Create one captions selector for each language that you want to include in the output, to a maximum of four selectors.

  • A combination of Embedded passthrough and Embedded conversion – If you are setting up for embedded passthrough in some outputs and embedded-to-other in other outputs, create one captions selector for each language that you want to include in the output, to a maximum of four selectors. Don't worry about a selector for the embedded passthrough output. MediaLive extracts all the languages for that output, even though there is not a selector to explicitly specify this action.

Captions selector fields

  • Selector settings:

    • Choose embedded if the source captions are embedded (EIA-608 or CEA-708), embedded+SCTE-20, or SCTE-20+embedded.

    • Choose SCTE-20 if the source captions are SCTE-20 alone.

  • EIA-608 track number – This field specifies the language to extract. Complete as follows:

    • If you are setting up for embedded passthrough only (you are creating only one captions selector for the input embedded captions), this field is ignored, so keep the default.

    • If you are converting embedded to another format (you are creating several captions selectors, one for each language), specify the number of the CC instance (from the input) that holds the language that you want.

  • Convert 608 to 708: The embedded source captions can be EIA-608 captions, CEA-708 captions, or both EIA-608 and CEA-708. You can specify how you want these captions to be handled when AWS Elemental MediaLive is ingesting content. The following table describes the behavior for various scenarios.

    EIA-608 in source

    CEA-708 in source

    Convert field

    Result

    Yes

    No

    Upconvert

    CEA-708 data is created based on the EIA-608 data. EIA-608 data is added as 608-compatibility bits in the CEA-708 data.
    Yes No

    Disabled

    Original EIA-608 is preserved.

    No

    Yes

    Upconvert

    Original CEA-708 is preserved.

    No Yes

    Disabled

    Original CEA-708 is preserved.

    Yes

    Yes

    Upconvert

    CEA-708 data is discarded. New CEA-708 data is created based on the EIA-608 data. EIA-608 data is added as 608-compatibility bits in the CEA-708 data.

    The new CEA-708 data will not include any CEA-708 formatting features.

    Not recommended.
    Yes Yes

    Disabled

    Original EIA-608 is preserved and original CEA-708 is preserved.

  • SCTE-20 detection – If the source captions combine embedded (EIA-608 or CEA-708) and SCTE-20, you might want to set this field to Auto. AWS Elemental MediaLive gives preference to the 608/708 embedded captions but switches to use the SCTE-20 captions when necessary. If you set this field to Off, AWS Elemental MediaLive never uses the SCTE-20 captions.

Information for Teletext

Teletext is a form of data that can contain several types of information, not just captions. Teletext can be handled in one of the following ways:

  • If you want to include the entire Teletext input, you must set up for Teletext passthrough. The entire Teletext can never be converted to another format.

  • Individual captions pages (the captions in a specific language) can be extracted and converted to another captions format.

  • Individual captions pages (the captions in a specific language) cannot be extracted and kept in Teletext. If you want to extract individual captions pages, you must convert them to another format.

How many captions selectors?

  • If you are setting up for Teletext passthrough captions, create only one captions selector, even if you want to include multiple languages in the output. With this scenario, all languages are automatically extracted and included in the output.

  • If you are setting up for Teletext-to-other, create one captions selector for each language that you want to include in the output. For example, one selector to extract English Teletext, and one selector to extract Swedish Teletext.

  • If you are setting up for Teletext passthrough in some outputs and Teletext-to-other in other outputs, create one captions selector for each language that you want to include in the output. Don't worry about a selector for the passthrough output. MediaLive passes through all the data, even though there isn't a selector to explicitly specify this action.

Captions selector fields

  • Selector settings – Choose Teletext.

  • Page number – This field specifies the page of the desired language. Complete as follows:

    • If you are setting up for Teletext passthrough captions (you are creating only one captions selector for the input captions), keep the field blank. The value is ignored.

    • If you are converting Teletext to another format (you are creating several captions selectors, one for each language), complete the Language code field to specify the page for the language that you want. If you leave this field blank, you get a validation error when you save the channel.

Including a positioning rectangle

If you plan to convert the source captions to EBU-TT-D, you can optionally define a rectangle that positions the captions on the video frame in the output. If you choose to use this feature, it will apply as follows:

  • It will apply to all your EBU-TT-D outputs that use this captions selector.

  • It won't apply to any other formats of output captions that use this caption selector. The positioning information is simply omitted from these other captions formats.

You define the rectangle relative to the underlying video frame. For example, you specify the position of the left edge of the rectangle as a percentage of the entire width of the video frame. A value of 10 means "calculate a value X that is 10% of the frame width. Then find the left edge of the video frame and move X pixels into the frame and draw the left edge of the rectangle".

Specifying a percentage, rather than a fixed number, means that the rectangle works for different video renditions (different resolutions) in the same output.

To define a positioning rectangle, follow this procedure.

  1. In the Output rectangle field, choose Caption rectangle.

  2. Complete the fields for the four sides of the rectangle – Left offset, Width, Top offset, and Height.