What is an Assembly?
A Transloadit Assembly executes Assembly Instructions on uploaded or imported files. Each execution has a unique `assembly_id` that identifies it in later API requests.
How Assemblies work
An Assembly is the runtime job created when a request combines source files with a processing graph. The service resolves inputs, schedules Robot work, records intermediate state, and gathers outputs under one execution identity. It differs from a reusable Template, which stores configuration rather than representing a particular run. Applications use the job boundary for monitoring, auditing, callback correlation, and result collection.
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.
Key facts
- 1One Assembly can fan a source file into multiple processing branches, and downstream Steps may consume the named results of earlier Steps within that same execution.
- 2The execution identifier is the stable correlation key across submission responses, status retrieval, logs, and completion notifications; Step names identify work inside it.
- 3A successfully accepted job can still finish with processing errors, so clients must inspect its terminal state and per-Step results instead of relying on HTTP acceptance alone.
When Assemblies matter
Store the `assembly_id` when a workflow must poll status, retrieve results, or correlate callbacks with a request. Losing that identifier makes later execution tracking and diagnosis more difficult.
- Running repeatable upload, import, processing, AI, storage, and notification pipelines.
- Tracking long-running media work independently from an application request.
- Applying credentials, quotas, retries, and error policies consistently across integrations.
Working with platform at scale
Guidance that holds across every platform term in this glossary, not just Assemblies.
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.
Answer these 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.
How Transloadit helps with Assemblies
When Assemblies are relevant to your workflow, you can hand the surrounding platform work to Transloadit instead of maintaining the processing stack yourself. Transloadit models file workflows as reusable Assembly Instructions. Upload, import, processing, AI, storage, delivery, status updates, and error handling can be composed without operating the underlying media tools yourself.
Support for a specific codec, container, parameter, or combination can vary by Robot and processing stack. Check the linked documentation for the exact inputs and outputs available for your use case.