Is there any way to save mulaw audio stream from twilio in a file - twilio

Question

I am using Twilio voice stream feature and i don't want to use Twilio record functionality. When Twilio starts sending voice stream to my server i want to store it into disk as an audio file in realtime.

Answer 1

I was running into the same issue today and figured a way to generate a WAVE Header for the mu-law header:
If you're following Twilio's blog post, that's the code I ended implementing:
wss.on('connection', (socket) => {
socket.on('message', (msg) => {
const { event, ...message } = JSON.parse(msg);
switch (event) {
case 'start':
let streamSid = message.start.streamSid;
socket.wstream = fs.createWriteStream(__dirname + `/${Date.now()}.wav`, { encoding: 'binary' });
// This is a mu-law header for a WAV-file compatible with twilio format
socket.wstream.write(Buffer.from([
0x52,0x49,0x46,0x46,0x62,0xb8,0x00,0x00,0x57,0x41,0x56,0x45,0x66,0x6d,0x74,0x20,
0x12,0x00,0x00,0x00,0x07,0x00,0x01,0x00,0x40,0x1f,0x00,0x00,0x80,0x3e,0x00,0x00,
0x02,0x00,0x04,0x00,0x00,0x00,0x66,0x61,0x63,0x74,0x04,0x00,0x00,0x00,0xc5,0x5b,
0x00,0x00,0x64,0x61,0x74,0x61,0x00,0x00,0x00,0x00, // Those last 4 bytes are the data length
]));
break;
case 'media':
// decode the base64-encoded data and write to stream
socket.wstream.write(Buffer.from(message.media.payload, 'base64'));
break;
case 'stop':
// Now the only thing missing is to write the number of data bytes in the header
socket.wstream.write("", () => {
let fd = fs.openSync(socket.wstream.path, 'r+'); // `r+` mode is needed in order to write to arbitrary position
let count = socket.wstream.bytesWritten;
count -= 58; // The header itself is 58 bytes long and we only want the data byte length
console.log(count)
fs.writeSync(
fd,
Buffer.from([
count % 256,
(count >> 8) % 256,
(count >> 16) % 256,
(count >> 24) % 256,
]),
0,
4, // Write 4 bytes
54, // starts writing at byte 54 in the file
);
});
break;
}
});
});

Answer 2

You can use FFmpeg to convert the Twilio mulaw to a regular WAV file.
If you use the class below, then you will just need to send the Twilio stream buffers when they arrive.
Something like:
recording = StreamAudioRecording(tempDirectory)
recording.start_recording(call_id)
<loop over buffer packets arriving>
recording.write_buffer(buffer)
recording_audio_path = recording.stop_recording()
This is the class implementation
import os
RAW_AUDIO_FILE_EXTENSION = "ulaw"
CONVERTED_AUDIO_FILE_EXTENSION = "wav"
class StreamAudioRecording:
def __init__(self, audio_recording_path):
self.audio_recording_path = audio_recording_path
self.f = None
self.audio_file_path = None
def start_recording(self, call_id):
self.audio_file_path = os.path.join(self.audio_recording_path, f" .
{call_id}.{RAW_AUDIO_FILE_EXTENSION}")
self.f = open(self.audio_file_path, 'wb')
def write_buffer(self, buffer):
self.f.write(buffer)
def stop_recording(self):
self.f.close()
converted_audio_path =
self.audio_file_path.replace(RAW_AUDIO_FILE_EXTENSION,
CONVERTED_AUDIO_FILE_EXTENSION)
self.convert_call_recording(self.audio_file_path, converted_audio_path)
return converted_audio_path
#staticmethod
def convert_call_recording(mulaw_path, wav_path):
command = f"ffmpeg -y -loglevel panic -f mulaw -ar 8k -ac 1 -i {mulaw_path} {wav_path}"
os.system(command)

Answer 3

If your using Node.js, the solution that #tdeo provided works great. I was inspired and I made a simple library using this solution. It's available now on npm.
https://www.npmjs.com/package/twilio-media-stream-save-audio-file