# Assembly Execution Progress

###### Warning

This feature is still in an experimental stage. Its exact behavior, its API, and its pricing might change while we are continuing to work on it. If you encounter any bugs or odd behavior, please [contact us](mailto:support@transloadit.com).

Assembly Execution Progress provides real-time estimates about how far the execution of anAssembly has progressed. A percentage value is calculated for the progress of the entire Assembly, as well as for each uploaded file (and any imports that include an `original_id`). This provides accurate progress information even if files are processed differently in the sameAssembly, for example because of different file type.

To calculate these percentage values, our Assembly engine predicts what Steps are likely to be executed for the remaining Assembly. This prediction is then compared to the already finished Steps to obtain the progress estimate. We then enhance this estimation by incorporating progress information from currently executingSteps. For example, for `/video/encode` Steps we include information about how much of the video has been encoded at the moment.

Assembly Execution Progress is a great enhancement for your user interface, providing your users insight into what's happening to their files. Combined with regular upload progress, which shows the progress for transferring the users' files to our servers, Assembly Execution Progress helps to let your users know that their files are taken care of and that the things are happening behind the scenes.

## Compatible Assemblies

We attempt to provide Execution Progressfor every Assembly, but this is not reliably possible for all cases. If your Assembly includes aStep, with an unpredictable result count, no progress can be estimated until this Step is completed. However, once all of these Steps are finished,Execution Progress can be calculated.

Steps whose result count cannot be predicted are:

* Importing directories via `/s3/import`, `/azure/import` etc. This does not include importing a fixed number of files.
* `/file/compress`: Extracting any type of archive.
* `/document/thumbs`: Generating thumbnails for a document without specifying the page number.

If your Assembly does not include suchSteps,Execution Progress is available from the beginning. If it does include such Steps, progress is available after these Steps are completed.

Execution Progress is not available for URL Transform Assemblies (the `emit_execution_progress` flag is ignored). For multipart uploads, progress can only start after upload metadata is extracted, which happens once uploads finish.

## Enabling Assembly Execution Progress

You must explicitly opt-in for each Assembly, for which you want to receive Execution Progress. This is performed when the [Assembly is created](/docs/api/assemblies-post.md) by including the`"emit_execution_progress": true` property in the Assembly Instructions, for example:

![](/_next/static/media/copy.04p1cju9qekk_.svg?dpl=dpl_CtwzFbHWtqiCy9uvWb9fE7WvfP9N)

```jsonc
{
  "steps": {
    "resized": {
      "robot": "/image/resize",
      "use": ":original",
      "width": 100,
      "height": 100,
      "resize_strategy": "fillcrop",
    },
    // ...
  },
  // ...

  // Enable execution progress
  "emit_execution_progress": true,
}

```

## Quickstart

1. Add `"emit_execution_progress": true` to your Assembly Instructions.
2. Open the [Assembly update stream](/docs/api/assemblies-assembly-id-stream-get.md).
3. Listen for the `assembly_execution_progress` event and update your UI.

## Receiving Execution Progress

Assembly Execution Progress can be retrieved with the Assembly update stream. In a nutshell, once an Assembly has been created, theAssembly Status contains a URL, where you can retrieve messages and events in real-time about the status of theAssembly. The exact details are described further in the[documentation](/docs/api/assemblies-assembly-id-stream-get.md).

Once the update stream for an Assembly is opened, andExecution Progress is enabled, you will receive progress updates regularly about every 2 seconds. The update is sent via the`assembly_execution_progress` event. It includes a JSON payload describing the progress for the entire Assembly and each original file (uploads and any imports that include an `original_id`), for example:

![](/_next/static/media/copy.04p1cju9qekk_.svg?dpl=dpl_CtwzFbHWtqiCy9uvWb9fE7WvfP9N)

```json
{
  "progress_combined": 75,
  "progress_per_original_file": [
    {
      "original_id": "6bb16f6cd49a44b4ae431f576e016c6d",
      "progress": 50
    },

    {
      "original_id": "56921a2dd46246d3b4d3a98b9f8ed4e1",
      "progress": 100
    }
  ]
}

```

In the above example, the entire Assembly is processed to 75%. The file with the `original_id` of `56921a2dd46246d3b4d3a98b9f8ed4e1` has finished processing, meaning it has progressed through all of its Steps. The file with the `original_id` of `6bb16f6cd49a44b4ae431f576e016c6d` is not yet done, with 50% progress so far.

If no progress estimate is available because the Assemblyincludes unfinished Steps, whose result count cannot be predicted, no event will be emitted until these Stepsare finished.