Add subtitles to videos

Usage example

{
  "steps": {
    "add_english_subtitles": {
      "robot": "/video/subtitle",
      "use": {
        "steps": [
          {
            "name": ":original",
            "fields": "input_video",
            "as": "video"
          },
          {
            "name": ":original",
            "fields": "input_srt_en",
            "as": "subtitles"
          }
        ]
      },
      "language": "eng",
      "name": "English",
      "ffmpeg_stack": "v6"
    },
    "add_german_subtitles": {
      "robot": "/video/subtitle",
      "use": {
        "steps": [
          {
            "name": "add_english_subtitles",
            "as": "video"
          },
          {
            : ,
            : ,
            : 
          }
        ]
      },
      : ,
      : ,
      : ,
      : 
    }
  }
}

Parameters

• interpolate

  boolean | Record<string, boolean>

• output_meta

  Record<string, boolean> | boolean | Array<string>

• result

  boolean (default: false)

• queue

  batch

• force_accept

  boolean (default: false)

• ignore_errors

  boolean | Array<meta | execute> (default: [])

• use

  string | Array<string> | Array<object> | object

• ffmpeg

  object

• ffmpeg_stack

  v6 | v7 | v8 | string (default: "v6.0.0")

• width

  string | number | null

• height

  string | number | null

• preset

  android | android-high | android-low | android_high | android_low | dash-1080p-video | dash-1080p_video | rKMa06

• subtitles_type

  burned | external | burn (default: "external")

• border_style

  box | outline | shadow (default: "outline")

• border_color

  string (default: "40000000")

• font

  string (default: "Arial")

• font_color

  string | string (default: "FFFFFF")

• font_size

  string | number (default: 16)

• bold

  boolean (default: false)

• italic

  boolean (default: false)

• outline_width

  string | number | null

• position

  bottom | bottom-left | bottom-right | center | left | right | top | rKMa06 (default: "bottom")

• language

  string | null

• name

  string | null

• keep_subtitles

  boolean (default: false)

Demos

Related blog posts

This Robot supports both SRT and VTT subtitle files.

If you have two file input fields in a form — one for a video and another for an SRT or VTT subtitle, named input_video and input_srt respectively (with the HTML name attribute), hereʼs how to embed the subtitles into the video with Transloadit:

Controls whether Assembly Variables are interpolated for individual instruction fields.

By default, most Robot instruction fields interpolate Assembly Variables. Set this to false to treat every instruction field as literal text, or set an individual field path to false to treat only that field as literal text. For Robot-specific fields that are literal by default, set this to true or set that field path to true to opt back into interpolation.

Use field names such as path, or dotted paths such as ffmpeg.vf for nested objects.

Whether the results of this Step should be present in the Assembly Status JSON

Setting the queue to 'batch', manually downgrades the priority of jobs for this step to avoid consuming Priority job slots for jobs that don't need zero queue waiting times

Force a Robot to accept a file type it would have ignored.

By default, Robots ignore files they are not familiar with. 🤖/video/encode, for example, will happily ignore input images.

With the force_accept parameter set to true, you can force Robots to accept all files thrown at them. This will typically lead to errors and should only be used for debugging or combatting edge cases.

Ignore errors during specific phases of processing.

Setting this to ["meta"] will cause the Robot to ignore errors during metadata extraction.

Setting this to ["execute"] will cause the Robot to ignore errors during the main execution phase.

Setting this to true is equivalent to ["meta", "execute"] and will ignore errors in both phases.

Specifies which Step(s) to use as input.

• You can pick any names for Steps except ":original" (reserved for user uploads handled by Transloadit)
• You can provide several Steps as input with arrays:
  

  {
    "use": [
      ":original",
      "encoded",
      "resized"
    ]
  }
  

• You can also tag input Steps with as to pass semantic intent to robots:
  

  {
    "use": [
      {
        "name": ":original",
        "as": "image"
      },
      {
        "name": ":original",
        "as": "mask"
      }
    ]
  }
  

A parameter object to be passed to FFmpeg. If a preset is used, the options specified are merged on top of the ones from the preset. For available options, see the FFmpeg documentation. Options specified here take precedence over the preset options.

Selects the FFmpeg stack version to use for encoding. These versions reflect real FFmpeg versions. We currently recommend to use "v6.0.0". Deprecated "v5.x" values are accepted for backward compatibility.

Width of the new video, in pixels.

If the value is not specified and the preset parameter is available, the preset's supplied width will be implemented.

Height of the new video, in pixels.

If the value is not specified and the preset parameter is available, the preset's supplied height will be implemented.

Determines if subtitles are added as a separate stream to the video (value "external") that then can be switched on and off in your video player, or if they should be burned directly into the video (value "burned" or "burn") so that they become part of the video stream.

Specifies the style of the subtitle. Use the border_color parameter to specify the color of the border.

The color for the subtitle border. The first two hex digits specify the alpha value of the color.

The font family to use. Also includes boldness and style of the font.

Here is a list of all supported fonts.

The color of the subtitle text in "rgb", "rrggbb", or "aarrggbb" format. If 8 hex digits are provided, the first two specify the alpha value of the color ("00" is fully opaque, "ff" is fully transparent).

Specifies the size of the text.

Specifies whether the subtitle text should be bold. Only applies to burned subtitles.

Specifies whether the subtitle text should be italic. Only applies to burned subtitles.

Specifies the width of the text outline in pixels. Only applies to burned subtitles with "outline" or "box" border styles. If not specified, the default width is used.

Specifies the position of the subtitles.

Specifies the language of the subtitle stream using a three-letter language code (e.g. "eng", "deu", "spa"). Only used if the subtitles are external. When adding multiple subtitle streams, set a different language for each stream so that video players can offer language selection.

Specifies a human-readable name for the subtitle track (e.g. "English", "Deutsch", "Español"). Only used if the subtitles are external. This name is displayed in video player subtitle menus alongside the language.

Specifies if existing subtitles in the input file should be kept or be replaced by the new subtitle. Only used if the subtitles are external. Set this to true when chaining multiple /video/subtitle Steps to add several subtitle streams (e.g. different languages) to the same video.

Allows you to specify a set of metadata that is more expensive on CPU power to calculate, and thus is disabled by default to keep your Assemblies processing fast.

For images, you can add "has_transparency": true in this object to extract if the image contains transparent parts and "dominant_colors": true to extract an array of hexadecimal color codes from the image.

For images, you can also add "blurhash": true to extract a BlurHash string — a compact representation of a placeholder for the image, useful for showing a blurred preview while the full image loads.

For videos, you can add the "colorspace: true" parameter to extract the colorspace of the output video.

For videos, you can also add "interlaced": true to detect whether the video is interlaced. This combines the cheap ffprobe field_order flag with a bounded idet sampling pass over the first frames of the source, exposing interlaced, field_order, and a diagnostic interlace_detection object under file.meta. This is computationally expensive and billed accordingly.

For audio, you can add "mean_volume": true to get a single value representing the mean average volume of the audio file.

You can also set this to false to skip metadata extraction and speed up transcoding.

Converts a video according to pre-configured settings.

If you specify your own FFmpeg parameters using the Robot's and/or do not not want Transloadit to set any encoding setting, starting ffmpeg_stack: "v6", you can use the value 'empty' here.