Audio processing using Pydub and Google speechRecognition API

Audio files are a widespread means of transferring information. So, let’s see how to break down audio files (.wav files) into smaller chunks, and to recognize the content in them and store it to a text file. To know more about audio files and their formats, refer Audio_formats.

Need to break down an audio file?

When we do any processing on audio files, it takes a lot of time. Here, processing can mean anything. For example, we may want to increase or decrease the frequency of the audio, or as done in this article, recognize the content in the audio file. By breaking it down into small audio files called chunks, we can ensure that the processing happens fast.

Required Installations:

pip3 install pydub
pip3 install audioread
pip3 install SpeechRecognition

There are majorly two steps in the program.

Step #1: It deals with slicing the audio files into small chunks of a constant interval. The slicing can be done with, or without overlap. Overlap means that the next chunk created will start from a constant time backward, so that during the slicing if any audio/word gets cut, it can be covered by this overlap. For example, if the audio file is 22 seconds, and the overlap is 1.5 seconds, the timing of these chunks will be:

  chunk1 : 0 - 5 seconds
  chunk2 : 3.5 - 8.5 seconds
  chunk3 : 7 - 12 seconds
  chunk4 : 10.5 - 15.5 seconds
  chunk5 : 14 - 19.5 seconds
  chunk6 : 18 - 22 seconds

We can ignore this overlap by setting the overlap to 0.

Step #2: It deals with working with the sliced audio file to do whatever the user requires. Here, for demonstration purposes, the chunks have been passed through the Google Speech recognition module, and the text has been written to a separate file. To understand how to use the Google Speech Recognition module to recognize the audio from a microphone, refer this. In this article, we will be using the sliced audio files to recognize the content.

Step #2 is done in a loop inside Step #1. As soon as the audio file is sliced into the chunk, the chunk is recognized. This process continues till the end of the audio file.


Input :  Geek.wav

Output : 
Screenshot of cmd running the code:

Text File: recognized

Below is the implementation:





# Import necessary libraries
from pydub import AudioSegment
import speech_recognition as sr
# Input audio file to be sliced
audio = AudioSegment.from_wav("1.wav")
Step #1 - Slicing the audio file into smaller chunks.
# Length of the audiofile in milliseconds
n = len(audio)
# Variable to count the number of sliced chunks
counter = 1
# Text file to write the recognized audio
fh = open("recognized.txt", "w+")
# Interval length at which to slice the audio file.
# If length is 22 seconds, and interval is 5 seconds,
# The chunks created will be:
# chunk1 : 0 - 5 seconds
# chunk2 : 5 - 10 seconds
# chunk3 : 10 - 15 seconds
# chunk4 : 15 - 20 seconds
# chunk5 : 20 - 22 seconds
interval = 5 * 1000
# Length of audio to overlap. 
# If length is 22 seconds, and interval is 5 seconds,
# With overlap as 1.5 seconds,
# The chunks created will be:
# chunk1 : 0 - 5 seconds
# chunk2 : 3.5 - 8.5 seconds
# chunk3 : 7 - 12 seconds
# chunk4 : 10.5 - 15.5 seconds
# chunk5 : 14 - 19.5 seconds
# chunk6 : 18 - 22 seconds
overlap = 1.5 * 1000
# Initialize start and end seconds to 0
start = 0
end = 0
# Flag to keep track of end of file.
# When audio reaches its end, flag is set to 1 and we break
flag = 0
# Iterate from 0 to end of the file,
# with increment = interval
for i in range(0, 2 * n, interval):
    # During first iteration,
    # start is 0, end is the interval
    if i == 0:
        start = 0
        end = interval
    # All other iterations,
    # start is the previous end - overlap
    # end becomes end + interval
        start = end - overlap
        end = start + interval 
    # When end becomes greater than the file length,
    # end is set to the file length
    # flag is set to 1 to indicate break.
    if end >= n:
        end = n
        flag = 1
    # Storing audio file from the defined start to end
    chunk = audio[start:end]
    # Filename / Path to store the sliced audio
    filename = 'chunk'+str(counter)+'.wav'
    # Store the sliced audio file to the defined path
    chunk.export(filename, format ="wav")
    # Print information about the current chunk
    print("Processing chunk "+str(counter)+". Start = "
                        +str(start)+" end = "+str(end))
    # Increment counter for the next chunk
    counter = counter + 1
    # Slicing of the audio file is done.
    # Skip the below steps if there is some other usage
    # for the sliced audio files.
Step #2 - Recognizing the chunk and writing to a file.
    # Here, Google Speech Recognition is used
    # to take each chunk and recognize the text in it.
    # Specify the audio file to recognize
    AUDIO_FILE = filename
    # Initialize the recognizer
    r = sr.Recognizer()
    # Traverse the audio file and listen to the audio
    with sr.AudioFile(AUDIO_FILE) as source:
        audio_listened = r.listen(source)
    # Try to recognize the listened audio
    # And catch expections.
        rec = r.recognize_google(audio_listened)
        # If recognized, write into the file.
        fh.write(rec+" ")
    # If google could not understand the audio
    except sr.UnknownValueError:
        print("Could not understand audio")
    # If the results cannot be requested from Google.
    # Probably an internet connection error.
    except sr.RequestError as e:
        print("Could not request results.")
    # Check for flag.
    # If flag is 1, end of the whole audio reached.
    # Close the file and break.
    if flag == 1:




As we can see in the above screenshot, all these chunks are stored in the local system. We have now successfully sliced the audio file with an overlap and recognized the content from the chunks.

Advantages of this method:

  • The interval can be set to any length depending on how long we need the chunks to be.
  • Overlap ensures that no data is lost even if any word is said precisely at the end of the interval.
  • The chunks can all be stored in different audio files and used later if need be.
  • Any processing which can be done on an audio file can be done in these chunks as well, as they are just audio files.

Disadvantages of this method:

  • Using Google Speech Recognition requires an active internet connection.
  • After the overlap, some text processing should be done to remove the duplicate words recognized.
  • The accuracy of Google Speech Recognition varies on a lot of factors like background noise, speaker’s accent etc.

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