Base64 encoding audio content

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 Cloud Storage bucket by specifying the storage object in the request's uri field.

Any audio data in the content field in HTTP requests must be in base64 format. This page describes how to convert audio from a binary file to base64-encoded data.

Using the command line

Within a gRPC request, you can simply write 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.

Most development environments contain a native base64 utility to encode a binary into ASCII text data. To encode a file:

Linux

Encode the file using the base64 command line tool, making sure to prevent line-wrapping by using the -w 0 flag:

base64 INPUT_FILE 
-w 0 > OUTPUT_FILE

macOS

Encode the file using the base64 command line tool:

base64 -i INPUT_FILE 
-o OUTPUT_FILE

Windows

Encode the file using the Base64.exe tool:

Base64.exe -e INPUT_FILE 
> OUTPUT_FILE

PowerShell

Encode the file using the Convert.ToBase64String method:

[Convert]::ToBase64String([IO.File]::ReadAllBytes("./ INPUT_FILE 
")) > OUTPUT_FILE

Create a JSON request file, inlining the base64-encoded data:

JSON

  { 
  
 "recognizer" 
 : 
  
 "projects/ PROJECT_ID 
/locations/global/recognizers/_" 
 , 
  
 "content" 
 : 
  
 "ZkxhQwAAACIQABAAAAUJABtAA+gA8AB+W8FZndQvQAyjv..." 
 }

Using client libraries

Embedding 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_file 
 ): 
 with 
 open 
 ( 
 audio_file 
 , 
 "rb" 
 ) 
 as 
 f 
 : 
 encoded_content 
 = 
 base64 
 . 
 b64encode 
 ( 
 f 
 . 
 read 
 ()) 
 return 
 encoded_content

Node.js

  // Read the file into memory. 
 var 
  
 fs 
  
 = 
  
 require 
 ( 
 'fs' 
 ); 
 var 
  
 audioFile 
  
 = 
  
 fs 
 . 
 readFileSync 
 ( 
 ' /full/path/to/audio/file.wav 
' 
 ); 
 // Convert the audio data to a Buffer and base64 encode it. 
 var 
  
 encoded 
  
 = 
  
 Buffer 
 . 
 from 
 ( 
 audioFile 
 ). 
 toString 
 ( 
 'base64' 
 );

Java

  // Import the Base64 encoding library. 
 import 
  
 org.apache.commons.codec.binary.Base64 
 ; 
 // Encode the audio. 
 byte 
 [] 
  
 audioData 
  
 = 
  
 Base64 
 . 
 encodeBase64 
 ( 
 audioFile 
 . 
 getBytes 
 ()); 
 String 
  
 encodedString 
  
 = 
  
 Base64 
 . 
 getEncoder 
 (). 
 encodeToString 
 ( 
 audioData 
 );

Go

  import 
  
 ( 
  
 "bufio" 
  
 "encoding/base64" 
  
 "io" 
  
 "os" 
 ) 
 // Open audio file. 
 f 
 , 
  
 _ 
  
 := 
  
 os 
 . 
 Open 
 ( 
 " /full/path/to/audio/file.wav 
" 
 ) 
 // Read entire audio into byte slice. 
 reader 
  
 := 
  
 bufio 
 . 
 NewReader 
 ( 
 f 
 ) 
 content 
 , 
  
 _ 
  
 := 
  
 io 
 . 
 ReadAll 
 ( 
 reader 
 ) 
 // Encode audio as base64. 
 base64 
 . 
 StdEncoding 
 . 
 EncodeToString 
 ( 
 content 
 )