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Zencoder automatically passes captions through from inputs to outputs, for supported formats. You can also specify a caption file (in SCC format) to add to outputs during transcoding.

Input formats supported for captions:

  • MP4/M4V video files that have caption tracks in CEA-608 format
  • SCC, DFXP, or SAMI files specified with the caption_url option

Output formats supported for captions:

  • MP4/M4V files, with caption track in CEA-608 format
  • HLS outputs (segmented outputs with H.264 video in TS format)

Captions can not currently be added to HLS outputs when transmuxing. See prepare_for_segmenting for information.

Note: The following restrictions currently apply to caption conversion:

For DFXP inputs:

  • UTF8 encoding is required for all special characters
  • Only the first language is converted (the first DIV tag)
  • Animation, layout, and region features are not supported
  • Styles can be inline or referenced by ID, but only the tts:textAlign property is applied
  • Nested DIV and P tags are ignored
  • SPAN tags are ignored
  • Explicit breaks may be inserted with BR tags
  • Only a single caption may be on-screen at any time (subsequent captions will end previous ones)

For SAMI inputs:

  • Only the first language listed is converted (the first class-selector style)
  • Inline styles are not supported
  • Layout-related styling tags (table, div, etc.) are not supported
  • Explicit breaks may be inserted by using separate P tags

Setting Default Description
caption_url none URL to an SCC, DFXP, or SAMI caption file to include in the output.
skip_captions false Don't add or pass through captions to the output file.