Convert real-time MP3 to 8000/mulaw in Python

Programming
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1

I’m working with an API that streams real-time audio in the MP3 format (44.1kHz/16bit) and I need to convert this stream to 8000/mulaw. I’m currently using PyDub and Python’s audioop module to decode and process each chunk of audio as it arrives, but I often encounter errors due to incomplete MP3 frames. A frame could potentially be split between two chunks, so I can’t decode them independently.

Does anyone have any ideas on how I can handle this? Is there a way to process an MP3 stream in real-time while converting to 8000/mulaw, possibly using a different library or approach?

Here’s a simplified version of my current code:

from pydub import AudioSegment
import audioop
import io

class StreamConverter:
    def __init__(self):
        self.state = None  
        self.buffer = b''  

    def convert_chunk(self, chunk):
        # Add the chunk to the buffer
        self.buffer += chunk

        # Try to decode the buffer
        try:
            audio = AudioSegment.from_mp3(io.BytesIO(self.buffer))
        except CouldntDecodeError:
            return None

        # If decoding was successful, empty the buffer
        self.buffer = b''

        # Ensure audio is mono
        if audio.channels != 1:
            audio = audio.set_channels(1)

        # Get audio data as bytes
        raw_audio = audio.raw_data

        # Sample rate conversion
        chunk_8khz, self.state = audioop.ratecv(raw_audio, audio.sample_width, audio.channels, audio.frame_rate, 8000, self.state)

        # μ-law conversion
        chunk_ulaw = audioop.lin2ulaw(chunk_8khz, audio.sample_width)

        return chunk_ulaw

# This is then used as follows:
for chunk in audio_stream:
    if chunk is not None:
        ulaw_chunk = converter.convert_chunk(chunk)
        # send ulaw_chunk to twilio api

I need help handling the issue of incomplete MP3 frames in the real-time streaming process while converting to 8000/mulaw. Is there an alternative library or approach that can help me achieve this?

2

To handle the issue of incomplete MP3 frames in real-time streaming while converting to 8000/mulaw, you can use the pydub library along with the pydub.exceptions.CouldntDecodeError exception. Here’s an alternative approach to handle this issue:

from pydub import AudioSegment
import audioop
import io

class StreamConverter:
    def __init__(self):
        self.state = None  
        self.buffer = b''  

    def convert_chunk(self, chunk):
        # Add the chunk to the buffer
        self.buffer += chunk

        try:
            # Keep processing the buffer until there are no incomplete frames
            while True:
                # Try to decode the buffer
                try:
                    audio = AudioSegment.from_mp3(io.BytesIO(self.buffer))
                except pydub.exceptions.CouldntDecodeError:
                    break

                # If decoding was successful, empty the buffer
                self.buffer = b''

                # Ensure audio is mono
                if audio.channels != 1:
                    audio = audio.set_channels(1)

                # Get audio data as bytes
                raw_audio = audio.raw_data

                # Sample rate conversion
                chunk_8khz, self.state = audioop.ratecv(raw_audio, audio.sample_width, audio.channels, audio.frame_rate, 8000, self.state)

                # μ-law conversion
                chunk_ulaw = audioop.lin2ulaw(chunk_8khz, audio.sample_width)

                return chunk_ulaw

        except KeyboardInterrupt:
            return None

# This is then used as follows:
converter = StreamConverter()
for chunk in audio_stream:
    if chunk is not None:
        ulaw_chunk = converter.convert_chunk(chunk)
        # send ulaw_chunk to twilio api

This code will keep processing the buffer until there are no incomplete frames left in the buffer. It uses a while True loop with a break statement to handle the incomplete frames.