Speech-to-Text Guide

Discover the core transcription features of Salad Transcription API. Learn how to utilize parameters like audio_stream_index, multichannel, return_as_file, timestamps, diarization, enhanced_accuracy, and automatic or explicit language selection.

Last Updated: August 24, 2026

Transcription API Features Guide

Introduction

Salad Transcription API offers a suite of powerful features to help you get the most out of your audio and video content. This guide covers the key transcription parameters you can use to customize your transcription outputs:

• Transcription Output Options:
  • audio_stream_index
  • return_as_file
  • sentence_level_timestamps
  • word_level_timestamps
• Speaker Identification:
  • multichannel
  • diarization
  • sentence_diarization
• Model Selection:
  • enhanced_accuracy
• Language Specification:
  • language_code

By properly utilizing these parameters, you can enhance the accuracy, efficiency, and usability of your transcriptions.

Transcription Parameters

1. return_as_file

Description

The return_as_file parameter allows you to receive your transcription output as a downloadable file URL. This is particularly useful when dealing with large responses, as it helps avoid issues with response size limitations.

• Default: false
• Type: boolean

Usage

Set "return_as_file": true in your request to receive the transcription output as a file URL.

Example:

"input": {
  "url": "https://example.com/path/to/file.mp3",
  "return_as_file": true
}

Note:

• If the response size exceeds 1 MB, the output will automatically be returned as a file URL, even if return_as_file is set to false.
• This helps ensure reliable delivery of large transcription outputs.

2. sentence_level_timestamps

Description

Include timestamps at the sentence level in your transcription output.

• Default: false
• Type: boolean

Usage

Set "sentence_level_timestamps": true to include sentence-level timestamps. Set to false if you do not need them.

Example:

"input": {
  "url": "https://example.com/path/to/file.mp3",
  "sentence_level_timestamps": true
}

Output Format

"sentence_level_timestamps": [
    {
        "text": "Welcome to our presentation.",
        "timestamp": [
            29.98,
            29.98
        ],
        "start": 29.98,
        "end": 29.98,
    }
],

3. word_level_timestamps

Description

Include timestamps for each word in your transcription output.

• Default: false
• Type: boolean

Usage

Set "word_level_timestamps": true to include word-level timestamps.

Example:

"input": {
  "url": "https://example.com/path/to/file.mp3",
  "word_level_timestamps": true
}

Output Format Word-level timestamps are provided in the word_segments array of the output.

"word_segments": [
    {
        "word": "I",
        "start": 4.963,
        "end": 5.024,
        "score": 0.597,
    },
    {
        "word": "understand",
        "start": 5.084,
        "end": 5.548,
        "score": 0.471,
    },
    {
        "word": "something.",
        "start": 6.073,
        "end": 6.376,
        "score": 0.295,
    }
]

4. diarization

Description

Enable speaker separation and identification at the word level.

• Default: false
• Type: boolean

Usage

Example:

"input": {
  "url": "https://example.com/path/to/file.mp3",
  "diarization": true
}

Output Format Speaker labels are included in both segments and word_segments when diarization is enabled.

"word_segments": [
    {
        "word": "I",
        "start": 4.963,
        "end": 5.024,
        "score": 0.597,
        "speaker": "SPEAKER_00"
    },
    {
        "word": "understand",
        "start": 5.084,
        "end": 5.548,
        "score": 0.471,
        "speaker": "SPEAKER_00"
    },
    {
        "word": "something.",
        "start": 6.073,
        "end": 6.376,
        "score": 0.295,
        "speaker": "SPEAKER_00"
    }
]

5. sentence_diarization

Description

Include speaker information at the sentence level.

• Default: false
• Type: boolean

Usage

Example:

"input": {
  "url": "https://example.com/path/to/file.mp3",
  "sentence_diarization": true
}

Output Format Speaker labels are included in the segments array when sentence_diarization is enabled.

"sentence_level_timestamps": [
    {
        "text": "I understand something.",
        "timestamp": [
            4.64,
            6.82
        ],
        "start": 4.64,
        "end": 6.82,
        "speaker": "SPEAKER_00"
    }
]

Note: If several speakers are identified in one sentence the most appearing one will be returned.

6. multichannel

Description

Preserve separate audio channels for channel-based diarization. This option is available on primary transcribe only.

• Default: false
• Type: boolean

If you have a multichannel audio file, set "multichannel": true. Enable the output behavior needed by your workflow:

• "diarization": true for word-level speaker/channel results.
• "sentence_diarization": true for sentence-level speaker/channel results.

Do not send multichannel to Transcription Lite.

Usage

"input": {
  "url": "https://example.com/path/to/file.wav",
  "multichannel": true,
  "word_level_timestamps": true,
  "diarization": true
}

Output Format (word-level) The output will include speaker and channel labels for each word.

"word_segments": [
  {
    "word": "Okay,",
    "start": 0.324,
    "end": 0.566,
    "timestamp": [
        0.324,
        0.566
    ],
    "speaker": "SPEAKER_0",
    "channel": 0
  }
]

Output Format (sentence-level) The output will include speaker and channel labels for each sentence.

"sentence_level_timestamps": [
  {
    "start": 0.324,
    "end": 1.335,
    "text": "Okay, how are you?",
    "speaker": "SPEAKER_0",
    "channel": "0",
    "score": 100.0
  }
]

7. language_code

Description

The language_code parameter selects a Whisper language code. Omit it or set it to null to use automatic detection.

• Default: null (automatic detection)
• Type: string or null

When a specific source language is intended, provide its Whisper code. Do not provide a guessed value; omit the field when automatic detection is the desired behavior.

Accuracy varies by language. For tested results, see our accuracy benchmarks.

Usage

Set the language_code to the ISO 639-1 code of the audio’s language.

Example:

"input": {
  "url": "https://example.com/path/to/french_audio.mp3",
  "language_code": "fr"
}

Supported Language Codes (ISO 639-1):

Code	Language	Code	Language	Code	Language
en	English	zh	Chinese	de	German
es	Spanish	ru	Russian	ko	Korean
fr	French	ja	Japanese	pt	Portuguese
tr	Turkish	pl	Polish	ca	Catalan
nl	Dutch	ar	Arabic	sv	Swedish
it	Italian	id	Indonesian	hi	Hindi
fi	Finnish	vi	Vietnamese	he	Hebrew
uk	Ukrainian	el	Greek	ms	Malay
cs	Czech	ro	Romanian	da	Danish
hu	Hungarian	ta	Tamil	no	Norwegian
th	Thai	ur	Urdu	hr	Croatian
bg	Bulgarian	lt	Lithuanian	la	Latin
mi	Maori	ml	Malayalam	cy	Welsh
sk	Slovak	te	Telugu	fa	Persian
lv	Latvian	bn	Bengali	sr	Serbian
az	Azerbaijani	sl	Slovenian	kn	Kannada
et	Estonian	mk	Macedonian	br	Breton
eu	Basque	is	Icelandic	hy	Armenian
ne	Nepali	mn	Mongolian	bs	Bosnian
kk	Kazakh	sq	Albanian	sw	Swahili
gl	Galician	mr	Marathi	pa	Punjabi
si	Sinhala	km	Khmer	sn	Shona
yo	Yoruba	so	Somali	af	Afrikaans
oc	Occitan	ka	Georgian	be	Belarusian
tg	Tajik	sd	Sindhi	gu	Gujarati
am	Amharic	yi	Yiddish	lo	Lao
uz	Uzbek	fo	Faroese	ht	Haitian Creole
ps	Pashto	tk	Turkmen	nn	Nynorsk
mt	Maltese	sa	Sanskrit	lb	Luxembourgish
my	Myanmar	bo	Tibetan	tl	Tagalog
mg	Malagasy	as	Assamese	tt	Tatar
haw	Hawaiian	ln	Lingala	ha	Hausa
ba	Bashkir	jw	Javanese	su	Sundanese
yue	Cantonese

Note

• Automatic Detection: Omit language_code or set it to null to enable automatic detection.
• Translation Option: Use "translate": "to_eng" for the only currently defined Whisper translation behavior.
• Multilingual Content: For multilingual audio, it is better not to specify a language to ensure the best results.

By setting the correct language_code or leveraging the automatic detection feature, you ensure the best possible transcription quality tailored to your audio content.

8. audio_stream_index

Use this field for MP4 or other multitrack media when you need a specific audio stream. It is a zero-based integer; omit it or set it to null when no explicit stream selection is needed.

"input": {
  "url": "https://example.com/path/to/file.mp4",
  "audio_stream_index": 1
}

9. enhanced_accuracy

Set this primary-only boolean to true to use a language-specific fine-tuned model when one is available. Its default is false; availability for a language must not be inferred from this setting alone.