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Our /video/subtitle Robot

Add subtitles to videos

🤖/video/subtitle adds subtitles and closed captions to videos.

This Robot supports both SRT and VTT subtitle files.

Usage example

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:

  "steps": {
    "subtitled": {
      "robot": "/video/subtitle",
      "use": {
        "steps": [
          { "name": ":original", "fields": "input_video", "as": "video" },
          { "name": ":original", "fields": "input_srt", "as": "subtitles" }
      "ffmpeg_stack": "v6.0.0"


  • use

    String / Array of Strings / Object required

    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": [

    💡 That’s likely all you need to know about use, but you can view Advanced use cases.

  • output_meta

    Object / Boolean ⋅ default: {}

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

    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.

  • preset

    String ⋅ default: "empty"

    Performs conversion using pre-configured settings. By default, no settings are applied and the original settings of the video are preserved.

    For a list of video presets, see video presets.

  • subtitles_type

    String ⋅ default: "external"

    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 "burn") so that they become part of the video stream.

  • border_style

    String ⋅ default: "outline"

    Specifies the style of the subtitle, from three options: outline, box, and shadow. Use the border_color parameter to specify the color of the border.

  • border_color

    String ⋅ default: "40000000"

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

  • font

    String ⋅ default: "Arial"

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

    Here is a list of all supported fonts.

  • font_color

    String ⋅ default: "00FFFFFF"

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

  • font_size

    Integer ⋅ default: 16

    Specifies the size of the text.

  • position

    String ⋅ default: bottom

    Specifies the position of the subtitles. The available options are "center", "top", "bottom", "left", and "right". You can also combine options, such as "bottom-right".

FFmpeg parameters

  • ffmpeg_stack

    String ⋅ default: "v5.0.0"

    Selects the FFmpeg stack version to use for encoding. These versions reflect real FFmpeg versions. We currently recommend to use "v6.0.0".

    Supported values: "v5.0.0", "v6.0.0".

    A full comparison of video presets, per stack, can be found here.

  • ffmpeg

    Object ⋅ default: {}

    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.


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