Supported Formats in Offline Transcription

For offline transcription Voicegain relies on the ffmpeg for converting input audio to the format suitable for the Speech-to-Text engine. Because of that we support a lot of audio formats in this scenario.
The complete list or supported audio formats is shown below.

Real-Time Transcription

For real-time transcription we support a smaller set of audio formats:

• PCMA: 8-bit a-law logarithmic
• PCMU: 8-bit u-law logarithmic - this is the G711 format
• L8: linear PCM 8-bit mono audio (signed little-endian)
• L16: linear PCM 16-bit mono audio (signed little-endian) - this is the format normally used in WAV files
• F32: linear PCM 32-bit floating point mono audio (little-endian) - audio captured from a web browser is typically in this format

Specifying Audio Parameters in API Requests

Audio field in API request will look e.g. like this:

"audio": {
  "source": {
    "inline": {
      "data": "dGhpcyBpcyB0aGUgZGF0YSB0aGF0IGlzIHRvIGJlIGVuY29kZWQgaW4gYmFzZSA2NA=="
    }
  },
  "format": "L16",
  "rate": 16000,
  "channels": "stereo",
  "capture": false
},

If the provided audio does not have an audio header (e.g. RIFF) then format, rate, channels are required.

For real-time  transcription, even if the audio has a header, there is still advantage to provide format, rate, channels if known because that speeds up the time for setup of the session - the audio header does not need to be examined.

Notes about the values:

• format - was already described in the previous section
• rate - the sample rate in Hz
• channels - possible values are "mono", "stereo" - specified the number of channels in the source audio
• capture - if set to true then the audio that has been processed will be captured. The uuid of the captured audio will be returned in the response. The uuid can be used to download the captured audio using this command: https://api.voicegain.ai/v1/data/<uuid>/file

Starting from version 1.16.0 channel selection from processing will be done using audioChannelSelector field. Possible values are "left", "right", "mix".