Inventory the calls you need to replace
Capslane v1 serves YouTube transcripts. Keep calls for other platforms, file URLs or unrelated metadata outside this migration. Check your actual provider adapter and SDK version, including any compatibility layer that changes status codes before responses reach the browser.
Supadata's current universal transcript reference is the comparison source, checked September 6, 2026. The table below specifies the Capslane target. It is not a guarantee that changing an SDK base URL makes every method compatible.
Map the target request and response
| Concern | Capslane target |
|---|---|
| Authentication | Create a Capslane key and send x-api-key. Provider keys are not interchangeable. |
| Initial request | GET https://capslane.com/v1/transcript with url set to a YouTube URL or 11-character ID. |
| Options | lang is a preference; text=true returns a string; chunkSize is 50 to 10,000 characters. |
| Modes | native never generates; auto generates after confirmed caption absence; generate selects audio. |
| Transcript | content, lang and availableLangs remain the main payload. Preserve source, cached and requestId for diagnostics. |
| Timing | offset and duration are milliseconds. Do not convert twice at an existing adapter boundary. |
| Accepted work | Store jobId from HTTP 202. Poll GET /v1/transcript/{jobId} using the Capslane key. |
| Errors | Normalize HTTP status and machine error code in your adapter; do not assume identical provider codes. |
curl 'https://capslane.com/v1/transcript?url=dQw4w9WgXcQ&lang=en&text=false&mode=auto' \
-H "x-api-key: $CAPSLANE_API_KEY"Set the environment variable outside source control. Test GET /v1/account first if you only need to validate the key. Choose text=false for products that use playback positions; switching to plain text discards the segmented representation your UI may require.
The Python and Node.js guides include complete HTTP examples. They handle immediate results and generated jobs without depending on a Supadata SDK.
Move the polling path and error adapter together
Persist the original job ID before polling. Use that same ID through intermediate states; do not rely on every response echoing it. Finish when content is available, and stop on failed, cancelled or your total deadline. If the original submission times out before returning an ID, inspect logs before blindly submitting again.
Capslane errors include a machine-readable error, a message and a request ID. Invalid input, disabled workspaces and depleted monthly allowances do not recover through immediate retries. Apply bounded backoff to transient upstream errors. Preserve a product-level distinction between unavailable captions and temporarily unreachable upstreams.
Count requests and generated minutes separately when comparing cost. Cached accepted requests still use the request allowance. Polls do not use another transcript request. Compare current plans against your observed workload instead of assuming the same billing unit between providers.
Define acceptance cases before changing traffic
- A public video with manual or automatic captions returns non-empty segments.
- A preferred language is either selected or a documented fallback is visible in the returned language.
- A repeated request preserves the expected text shape and reports cache use.
- A captionless video in native mode returns an unavailable error without audio generation.
- The same supported video in auto mode can reach a completed job when quota and capacity allow.
- Invalid, removed and unsupported inputs reach the correct product error state.
- Representative short and long videos retain usable playback offsets.
The public native corpus is a starting point for transport checks. Add your own authorized captionless and product-specific cases. A native-only HTTP benchmark cannot validate generation quality or your UI.
Check the two paths your product consumes
For native footage search, request segments and verify that a known offset still opens the correct point in the player. For a user-submitted captionless video, verify that the pending state reaches a complete transcript and that a failed job reaches an error state. A successful initial request alone leaves that second path untested.
Gems exercises these two cases separately. Start with the public native preview, then use the authenticated Playground for a complete response. Copy the final JSON into a private adapter fixture, replacing video text with synthetic test content before committing it. Do not keep production credentials or user transcript text in the fixture.
The HTTP-to-Markdown workflow is also a small independent consumer for checking segmented output. Keep its native mode when comparing extraction alone; it deliberately does not start generation or claim provider-wide compatibility.
Switch with observable rollback
Run a bounded shadow sample without duplicate downstream writes. Record status, source, latency and request ID; keep transcript text out of comparison logs. Review failures and a manual timing sample before routing real customer requests.
Move the provider adapter in a controlled release, retain the previous configuration for rollback and monitor both synchronous responses and final job outcomes. Verify your actual product flow after deployment. Gems used this approach for native footage search and the user transcript flow; the case study documents the scope and verification without inventing savings or customer-volume claims.