G.711 μ-law Encoder (Run)¶
This article explains how you can use Transcoder.Run to encode a WAV file to G.711 μ-law compressed audio format.
The code snippets in this article are from the enc_g711_ulaw_file sample.
Source Audio¶
For source we use the express-dictate_8000_s16_1ch_pcm.wav file from the AVBlocks Assets repository. After downloading and unzipping you will find express-dictate_8000_s16_1ch_pcm.wav in the aud subdirectory.
Code¶
This code takes a WAV file and encodes it to compressed G.711 μ-law format.
Initialize AVBlocks¶
The first step in any AVBlocks application is to initialize the library. This must be done before using any other AVBlocks functionality. The Library.Initialize() method sets up the internal state and loads necessary codecs. Always remember to call Library.Shutdown() at the end of your program to properly clean up resources and release any allocated memory.
static int Main(string[] args)
{
var opt = new Options();
if (!opt.Prepare(args))
return opt.Error ? (int)ExitCodes.OptionsError : (int)ExitCodes.Success;
Library.Initialize();
// Set license information. Without this AVBlocks runs in Demo mode.
// Library.SetLicense("<license-string>");
bool encodeResult = Encode(opt);
Library.Shutdown();
return encodeResult ? (int)ExitCodes.Success : (int)ExitCodes.EncodingError;
}
Configure Output Socket¶
The output socket defines where and how the encoded audio data will be written. In this case, we’re configuring it to output a G.711 μ-law WAV file. The socket represents the output destination, while the pin represents the specific audio stream within that destination. The AudioStreamInfo object specifies the audio format parameters - G.711 μ-law typically uses 8000 Hz sample rate and mono channel, which are set explicitly in this example.
static MediaSocket CreateOutputSocket(Options opt)
{
MediaSocket socket = new MediaSocket();
socket.File = opt.OutputFile;
socket.StreamType = StreamType.Wave;
MediaPin pin = new MediaPin();
socket.Pins.Add(pin);
AudioStreamInfo asi = new AudioStreamInfo();
pin.StreamInfo = asi;
asi.StreamType = StreamType.MuLawPCM;
// G.711 μ-law typically uses 8000 Hz sample rate and mono channel
asi.SampleRate = 8000;
asi.Channels = 1;
return socket;
}
Configure Transcoder and Encode¶
This is the main encoding function that ties everything together. First, we create an input socket that points to the WAV file we want to encode. Then we create the output socket using our helper method. The transcoder is the core component that performs the actual encoding - it takes the uncompressed PCM data from the input and converts it to compressed G.711 μ-law data for the output.
The AllowDemoMode = true setting allows the transcoder to work even without a valid license (useful for testing, but not recommended for production). We then add our input and output sockets to the transcoder, open it to prepare for processing, run the actual transcoding operation, and finally close it to clean up.
static bool Encode(Options opt)
{
// transcoder will fail if output exists (by design)
DeleteFile(opt.OutputFile);
// Create output directory if needed
string outputDir = System.IO.Path.GetDirectoryName(opt.OutputFile);
if (!string.IsNullOrEmpty(outputDir))
System.IO.Directory.CreateDirectory(outputDir);
// create input socket
MediaSocket inSocket = new MediaSocket();
inSocket.File = opt.InputFile;
// create output socket
MediaSocket outSocket = CreateOutputSocket(opt);
// create Transcoder
using (Transcoder transcoder = new Transcoder())
{
transcoder.AllowDemoMode = true;
transcoder.Inputs.Add(inSocket);
transcoder.Outputs.Add(outSocket);
bool res = transcoder.Open();
PrintError("Transcoder open", transcoder.Error);
if (!res)
return false;
res = transcoder.Run();
PrintError("Transcoder run", transcoder.Error);
if (!res)
return false;
transcoder.Close();
}
return true;
}
Complete C# Code¶
Here’s the complete working example that demonstrates G.711 μ-law encoding using AVBlocks. This code combines all the previous snippets into a functional program that can be compiled and run. The Main method handles command-line argument parsing, initializes AVBlocks, performs the encoding operation, and properly shuts down the library before exiting.
using System;
using PrimoSoftware.AVBlocks;
namespace CliSample
{
class Program
{
static int Main(string[] args)
{
var opt = new Options();
if (!opt.Prepare(args))
return opt.Error ? (int)ExitCodes.OptionsError : (int)ExitCodes.Success;
Library.Initialize();
// Set license information. Without this AVBlocks runs in Demo mode.
// Library.SetLicense("<license-string>");
bool encodeResult = Encode(opt);
Library.Shutdown();
return encodeResult ? (int)ExitCodes.Success : (int)ExitCodes.EncodingError;
}
static bool Encode(Options opt)
{
// transcoder will fail if output exists (by design)
DeleteFile(opt.OutputFile);
// Create output directory if needed
string outputDir = System.IO.Path.GetDirectoryName(opt.OutputFile);
if (!string.IsNullOrEmpty(outputDir))
System.IO.Directory.CreateDirectory(outputDir);
// create input socket
MediaSocket inSocket = new MediaSocket();
inSocket.File = opt.InputFile;
// create output socket
MediaSocket outSocket = CreateOutputSocket(opt);
// create Transcoder
using (Transcoder transcoder = new Transcoder())
{
transcoder.AllowDemoMode = true;
transcoder.Inputs.Add(inSocket);
transcoder.Outputs.Add(outSocket);
bool res = transcoder.Open();
PrintError("Transcoder open", transcoder.Error);
if (!res)
return false;
res = transcoder.Run();
PrintError("Transcoder run", transcoder.Error);
if (!res)
return false;
transcoder.Close();
}
return true;
}
static void DeleteFile(string filename)
{
try
{
if (System.IO.File.Exists(filename))
System.IO.File.Delete(filename);
}
catch { }
}
static MediaSocket CreateOutputSocket(Options opt)
{
MediaSocket socket = new MediaSocket();
socket.File = opt.OutputFile;
socket.StreamType = StreamType.Wave;
MediaPin pin = new MediaPin();
socket.Pins.Add(pin);
AudioStreamInfo asi = new AudioStreamInfo();
pin.StreamInfo = asi;
asi.StreamType = StreamType.MuLawPCM;
// G.711 μ-law typically uses 8000 Hz sample rate and mono channel
asi.SampleRate = 8000;
asi.Channels = 1;
return socket;
}
static void PrintError(string action, ErrorInfo e)
{
if (action != null)
{
Console.Write("{0}: ", action);
}
if (ErrorFacility.Success == e.Facility)
{
Console.WriteLine("Success");
return;
}
else
{
Console.WriteLine("{0}, facility:{1} code:{2} hint:{3}", e.Message ?? "", e.Facility, e.Code, e.Hint ?? "");
}
}
enum ExitCodes : int
{
Success = 0,
OptionsError = 1,
EncodingError = 2,
}
}
}
How to Run¶
See the build instructions for Windows, macOS, and Linux, and the enc_g711_ulaw_file sample for details.
Command Line¶
enc_g711_ulaw_file --input <wav file> --output <g711 ulaw wav file>
Examples¶
List options:
./bin/net10.0/enc_g711_ulaw_file --help
enc_g711_ulaw_file 1.0.0.0
Copyright (C) 2023 Primo Software
-i, --input input WAV file
-o, --output output G.711 μ-law WAV file
--help Display this help screen.
--version Display version information.
The following example encodes input file ./assets/aud/express-dictate_8000_s16_1ch_pcm.wav into output file express-dictate_g711_ulaw.wav:
# Linux and macOS
mkdir -p ./output/enc_g711_ulaw_file
./bin/net10.0/enc_g711_ulaw_file \
--input ./assets/aud/express-dictate_8000_s16_1ch_pcm.wav \
--output ./output/enc_g711_ulaw_file/express-dictate_g711_ulaw.wav
# Windows
mkdir -Force -Path ./output/enc_g711_ulaw_file
./bin/net10.0/enc_g711_ulaw_file `
--input ./assets/aud/express-dictate_8000_s16_1ch_pcm.wav `
--output ./output/enc_g711_ulaw_file/express-dictate_g711_ulaw.wav