What is Assembly Execution Progress?
Transloadit Assembly Execution Progress estimates an Assembly’s completion in real time for Assemblies that opt in with the emit_execution_progress parameter. Percentages are calculated from the Assembly’s Steps and may describe overall execution or an individual file.
How Assembly Execution Progress works
Execution progress aggregates how far scheduled work has advanced across a graph whose branches may differ greatly in cost. The displayed value is derived from Step and file activity rather than from a simple wall-clock countdown, so it may advance unevenly, and parallel branches can make it appear to pause while a costly operation runs. Progress is not emitted for URL Transform Assemblies. Overall progress summarizes the job, whereas file-level progress can expose a slow or blocked item. Interfaces consume the estimate for feedback while status data remains the authority on completion.
Key facts
- 1A late transcoding Step can account for much more real time than an earlier metadata Step, so equal percentage increments do not imply equal remaining durations.
- 2Progress events are emitted only when the Assembly’s parameters set
emit_execution_progressto true, and they are delivered over the realtime connection; polling the Assembly Status document alone will not surface these percentages. - 3A Step that is still executing reports capped progress (95%) because finishing work such as metadata extraction and result storage remains. Confirm completion only from terminal Assembly status; a failed or canceled branch is not a successful 100%.
When Assembly Execution Progress matters
Enable emit_execution_progress and listen for the progress events on the realtime connection when users need feedback during long processing jobs; the percentages arrive as streamed events rather than as a field in the polled Assembly Status. Treat the percentage as an estimate rather than elapsed time, because Steps can have unequal or unpredictable durations.
Common use cases for platform workflows
These examples cover platform workflows broadly, not specifically Assembly Execution Progress.
- Running repeatable upload, import, processing, AI, storage, and notification pipelines.
- Tracking long-running media work independently from an application request.
- Referencing centrally stored credentials by name instead of sending storage secrets with each request.
Working with platform workflows
This guidance covers platform workflows broadly, not just Assembly Execution Progress.
A client authenticates and submits files or references together with workflow instructions. The platform validates the request, schedules dependent operations, records state transitions, and exposes results through a response, polling endpoint, or notification.
Platform concepts become reliable only when their lifecycle is explicit. Authentication, idempotency, retries, timeouts, observability, quotas, and terminal states should be designed together rather than added after failures occur.
What you gain
- Reusable workflows separate application intent from processing infrastructure.
- Stable job identifiers and lifecycle events improve observability and recovery.
- Managed queues and workers let products scale without embedding every media tool.
What it costs
- Synchronous responses are simple but keep connections open while long work executes.
- Aggressive retries improve recovery from transient faults but can duplicate work or overload a dependency.
- Higher concurrency reduces queue time until resource contention or a downstream limit becomes the bottleneck.
Before production
- 1Define authentication, authorization, idempotency, retries, and terminal error behavior.
- 2Observe queue time, execution time, callbacks, and partial results with stable identifiers.
- 3Exercise malformed, duplicate, interrupted, and unauthorized requests before launch.