When you send audio data to the Speech-to-Text API you can either send the
data directly (within the request's
content
field) or
have the API perform recognition remotely on data stored in a Google Cloud
Storage bucket. You can send data directly in the content
field for
synchronous recognition
only if your audio data is a maximum of 60 seconds and 10 MB. Any audio
data in the content
field must be in base64 format. This page describes how to
convert audio from a binary file to base64-encoded data.
If your audio data exceeds 60 seconds or 10 MB, it must be stored in a Google Cloud Storage bucket in order to be sent for recognition. You can analyze it asynchronously without converting it to base64 format. See the asynchronous recognition documentation for details.
Embedding base64 encoded audio
Audio data is binary data. Within a gRPC request, you can simply write the binary data out directly; however, JSON is used when making a REST request. JSON is a text format that does not directly support binary data, so you will need to convert such binary data into text using Base64 encoding.
To base64 encode an audio file:
Linux
- Encode the audio file using the base64 command line tool, making sure to
prevent line-wrapping by using the
-w 0
flag:
$ base64 source_audio_file -w 0 > dest_audio_file
2. Create a JSON request file, inlining the base64-encoded audio within the
request's content
field:
{ "config": { "encoding":"FLAC", "sampleRateHertz":16000, "languageCode":"en-US" }, "audio": { "content": "ZkxhQwAAACIQABAAAAUJABtAA+gA8AB+W8FZndQvQAyjv..." } }
Mac OSX
- Encode the audio file using the base64 command line tool:
$ base64 source_audio_file > dest_audio_file
2. Create a JSON request file, inlining the base64-encoded audio within the
request's content
field:
{ "config": { "encoding":"FLAC", "sampleRateHertz":16000, "languageCode":"en-US" }, "audio": { "content": "ZkxhQwAAACIQABAAAAUJABtAA+gA8AB+W8FZndQvQAyjv..." } }
Windows
- Encode the audio file using the Base64.exe tool:
C:> Base64.exe -e source_audio_file > dest_audio_file
2. Create a JSON request file, inlining the base64-encoded audio within the
request's content
field:
{ "config": { "encoding":"FLAC", "sampleRateHertz":16000, "languageCode":"en-US" }, "audio": { "content": "ZkxhQwAAACIQABAAAAUJABtAA+gA8AB+W8FZndQvQAyjv..." } }
Embedding audio content programmatically
Embedding audio binary data into requests through text editors is neither desirable or practical. In practice, you will be embedding base64 encoded files within client code. All supported programming languages have built-in mechanisms for base64-encoding content:
Python
In Python, base64 encode audio files as follows:
# Import the base64 encoding library.
import base64
# Pass the audio data to an encoding function.
def encode_audio(audio):
audio_content = audio.read()
return base64.b64encode(audio_content)
Node.js
In Node.js, base64 encode audio files as follows, where audioFile
is the binary-encoded audio data:
Java
In Java, use the encodeBase64
static method within
org.apache.commons.codec.binary.Base64
to base64 encode binary files:
// Import the Base64 encoding library.
import org.apache.commons.codec.binary.Base64;
// Encode the speech.
byte[] encodedAudio = Base64.encodeBase64(audio.getBytes());