> ## Documentation Index
> Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Speech-to-Text REST API audio formats

> Supported audio formats for the Telnyx Speech-to-Text REST API — WAV, MP3, FLAC, OGG, and more. Includes recommended sample rates and encodings.

Applies to both `file` (multipart upload) and `file_url` (URL download).

## Common

* **Max size:** 100 MB
* **Processing:** All audio is decoded, resampled to 16kHz, and mixed to mono via ffmpeg before transcription. Container format doesn't matter as long as ffmpeg can decode it — the validated extension list is the actual restriction.

## Supported Formats

| Format | `whisper-turbo` | `whisper-tiny` | `deepgram/nova-3` |
| ------ | --------------- | -------------- | ----------------- |
| flac   | Yes             | Yes            | No                |
| m4a    | Yes             | Yes            | No                |
| mp3    | Yes             | Yes            | **Yes**           |
| mp4    | Yes             | Yes            | No                |
| mpeg   | Yes             | Yes            | No                |
| mpga   | Yes             | Yes            | No                |
| oga    | Yes             | Yes            | No                |
| ogg    | Yes             | Yes            | No                |
| wav    | Yes             | Yes            | **Yes**           |
| webm   | Yes             | Yes            | No                |

## `file` vs `file_url`

|            | `file`                           | `file_url`                                                  |
| ---------- | -------------------------------- | ----------------------------------------------------------- |
| Delivery   | Multipart upload in request body | Server downloads from URL before transcription              |
| Timeout    | Request timeout                  | 15s download timeout                                        |
| Auth       | N/A                              | URL must be publicly accessible (no auth headers forwarded) |
| Validation | Same format and size checks      | Same format and size checks                                 |

One of `file` or `file_url` is required. Sending both returns 400.