The /audio/loop Robot

We offer a variety of features to reduce audio size while maintaining quality, as well as add effects like loops or watermarks.

The /audio/loop Robot loops one audio file as often as is required to match a given duration.

Whether you're producing beats, white-noise, or just empty segments as fillers between audio tracks that you're to stringing together with our /audio/concat Robot, /audio/loop has got you're back.

Parameters

Name Type Default Description
use (required) String / Array of Strings / Object

General

Specifies which Step(s) to use as our input.

Special Step names

A special Step name is ":original", which provides user uploads handled by Transloadit. Outside of this restriction you can pick your own names.

Providing several Steps as input

You can add arrays to use several Steps:
"use": [
  ":original",
  "encoded",
  "resized"
]
:bulb: 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 use 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,
    }
  ]
}
preset String "mp3" Performs conversion using pre-configured settings. If you specify your own FFmpeg parameters using the Robot's ffmpeg parameter and you have not specified a preset, then the default mp3 preset is not applied. This is to prevent you from having to override each of the mp3 preset's values manually. For a list of audio presets, see audio presets.
bitrate Integer Auto Bit rate of the resulting audio file, in bits per second. If not specified will default to the bit rate of the input audio file
sample_rate Integer Auto Sample rate of the resulting audio file, in Hertz. If not specified will default to the sample rate of the input audio file
duration Float 60.0 Target duration for the whole process in seconds. The Robot will loop the input audio file for as long as this target duration is not reached yet.
FFmpeg Parameters
Name Type Default Description
ffmpeg_stack String "v1.0.0" Selects the FFmpeg stack version to use for encoding. These versions do not reflect any real FFmpeg versions, they reflect our own internal (non-semantic) versioning for our custom FFmpeg builds. The current recommendation is to use "v3.3.3" Other valid values can be found here. If you use ffmpeg_stack in conjunction with the /video/subtitle Robot, the default becomes "v3.3.3". Stack "v3.3.3" has a known regression when encoding to AIFF files with the alaw compression. If you need this, best use "v2.2.3".
ffmpeg Object {} 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.

Demos

Our /audio/loop Robot can be used in combination with other Robots, to create powerful workflows unique to your use case. Here are a few example scenarios that you can try live on our website:

Pricing

Transloadit is a SaaS with a subscription model.

We offer a discount of 75%, effectively counting only every fourth byte of audio files that you loop with /audio/loop. It charges at minimum 0MB whenever it is used. Assuming the Startup Plan and an average audio file size of 3.8MB, you could loop 2874 audio files for $49/month.

Just like with your mobile plan, pricing goes down considerably when you commit to larger monthly volumes. You can adjust this every month. More info and available plans on our Pricing page.

Blog posts about the /audio/loop Robot

We wrote the following posts about the /audio/loop Robot on our blog: