Generate waveform images from audio

We recommend that you use an /audio/encode Step prior to your waveform Step to convert audio files to MP3. This way it is guaranteed that the /audio/waveform Robot accepts your audio file and you can also down-sample large audio files and save some money.

Similarly, if you need the output image in a different format, please pipe the result of this Robot into the /image/resize Robot.

Here is an example waveform image:

Parameters

• 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": [
      ":original",
      "encoded",
      "resized"
    ]
    

  That’s likely all you need to know about use, but you can view advanced use cases:

  › Advanced use cases

  • Step bundling. Some Robots can gather several Step results for a single invocation. For example, the /file/compress Robot would normally create one archive for each file passed to it. If you'd set bundle_steps to true, however, it will create one archive containing all the result files from all Steps you give it. To enable bundling, provide an object like the one below to the use parameter:

    "use": {
      "steps": [
        ":original",
        "encoded",
        "resized"
      ],
      "bundle_steps": true
    }
    

    This is also a crucial parameter for the /video/adaptive Robot, otherwise you'll generate 1 playlist for each viewing quality.
    Keep in mind that all input Steps must be present in your Template. If one of them is missing (for instance it is rejected by a filter), no result is generated because the Robot waits indefinitely for all input Steps to be finished.

    Here’s a demo that showcases Step bundling.

  • Group by original. Sticking with the /file/compress Robot example, you can set group_by_original to true, in order to create a separate archive for each of your uploaded or imported files, instead of creating one archive containing all originals (or one per resulting file). This is important for for the /media/playlist Robot where you'd typically set:

    "use": {
      "steps": [
        "segmented"
      ],
      "bundle_steps": true,
      "group_by_original": true
    }
    

  • Fields. You can be more discriminatory by only using files that match a field name by setting the fields property. When this array is specified, the corresponding Step will only be executed for files submitted through one of the given field names, which correspond with the strings in the name attribute of the HTML file input field tag for instance. When using a back-end SDK, it corresponds with myFieldName1 in e.g.: $transloadit->addFile('myFieldName1', './chameleon.jpg').

    This parameter is set to true by default, meaning all fields are accepted.

    Example:

    "use": {
      "steps": [ ":original" ],
      "fields": [ "myFieldName1" ]
    }
    

  • Use as. Sometimes Robots take several inputs. For instance, the /video/merge Robot can create a slideshow from audio and images. You can map different Steps to the appropriate inputs.

    Example:

    "use": {
      "steps": [
        { "name": "audio_encoded", "as": "audio" },
        { "name": "images_resized", "as": "image" }
      ]
    }
    

    Sometimes the ordering is important, for instance, with our concat Robots. In these cases, you can add an index that starts at 1. You can also optionally filter by the multipart field name. Like in this example, where all files are coming from the same source (end-user uploads), but with different <input> names:

    Example:

    "use": {
      "steps": [
        { "name": ":original", "fields": "myFirstVideo", "as": "video_1" },
        { "name": ":original", "fields": "mySecondVideo", "as": "video_2" },
        { "name": ":original", "fields": "myThirdVideo", "as": "video_3" }
      ]
    }
    

    For times when it is not apparent where we should put the file, you can use Assembly Variables to be specific. For instance, you may want to pass a text file to the /image/resize Robot to burn the text in an image, but you are burning multiple texts, so where do we put the text file? We specify it via ${use.text_1}, to indicate the first text file that was passed.

    Example:

    "watermarked": {
      "robot": "/image/resize",
      "use"  : {
        "steps": [
          { "name": "resized", "as": "base" },
          { "name": "transcribed", "as": "text" },
        ],
      },
      "text": [
        {
          "text"  : "Hi there",
          "valign": "top",
          "align" : "left",
        },
        {
          "text"    : "From the 'transcribed' Step: ${use.text_1}",
          "valign"  : "bottom",
          "align"   : "right",
          "x_offset": 16,
          "y_offset": -10,
        }
      ]
    }
    

• format

  String ⋅ default: "image"

  The format of the result file. Can be "image" or "json". If "image" is supplied, a PNG image will be created, otherwise a JSON file.

• width

  Integer ⋅ default: 256

  The width of the resulting image if the format "image" was selected.

• height

  Integer ⋅ default: 64

  The height of the resulting image if the format "image" was selected.

• background_color

  String ⋅ default: "00000000"

  The background color of the resulting image in the "rrggbbaa" format (red, green, blue, alpha), if the format "image" was selected.

• center_color

  String ⋅ default: "000000ff"

  The color used in the center of the gradient. The format is "rrggbbaa" (red, green, blue, alpha).

• outer_color

  String ⋅ default: "000000ff"

  The color used in the outer parts of the gradient. The format is "rrggbbaa" (red, green, blue, alpha).

Demos

• Generate a waveform image from an audio file

Related blog posts

• Let's Build: Music Card Generator May 5, 2022
• Kicking Transloadit Into Gear for the New Year February 1, 2015
• Adding Support for Waveform Images November 22, 2012