Fun with Opus

Opus is a very popular, royalty-free audio codec. I thought I'd write a quick program showing how to use it for working with audio.

For this exercise, we're going to be using C++ on Windows.

Building blocks

Before we go too deep into opus, however, it'll be useful to be able to have a little utility to actually play audio.

Here's a quick adaptation of this sample we can use. Simply copy over the WAVFileReader.cpp and WAVFileReader.h files into the same directory, and use them like so, adjusting the path as needed.

#define WIN32_LEAN_AND_MEAN
#define NOMINMAX
#include <Windows.h>
#include <cstdio>
#include <memory>

#include <xaudio2.h>

#include <wrl\client.h>

namespace mwrl = Microsoft::WRL;

#define IFC(x) do { hr = x; if (FAILED(hr)) { goto Cleanup; } } while (false)

#include "WAVFileReader.h"

HRESULT PlayWave(IXAudio2 * pXaudio2, LPCWSTR szFilename)
{
  HRESULT hr = S_OK;
  BOOL isRunning = TRUE;
  std::unique_ptr<uint8_t[]> waveFile;
  DirectX::WAVData waveData;
  XAUDIO2_BUFFER buffer = {};
  IXAudio2SourceVoice* pSourceVoice = nullptr;

  IFC(DirectX::LoadWAVAudioFromFileEx(szFilename, waveFile, waveData));
  IFC(pXaudio2->CreateSourceVoice(&pSourceVoice, waveData.wfx));

  // Submit the wave sample data using an XAUDIO2_BUFFER structure
  buffer.pAudioData = waveData.startAudio;
  buffer.Flags = XAUDIO2_END_OF_STREAM;  // tell the source voice not to expect any data after this buffer
  buffer.AudioBytes = waveData.audioBytes;
  IFC(pSourceVoice->SubmitSourceBuffer(&buffer));
  IFC(pSourceVoice->Start(0));

  // Let the sound play
  while (SUCCEEDED(hr) && isRunning)
  {
    XAUDIO2_VOICE_STATE state;
    pSourceVoice->GetState(&state);
    isRunning = (state.BuffersQueued > 0) != 0;

    // Wait till the escape key is pressed
    if (GetAsyncKeyState(VK_ESCAPE))
        break;

    Sleep(10);
  }

  // Wait till the escape key is released
  while (GetAsyncKeyState(VK_ESCAPE))
    Sleep(10);

  pSourceVoice->DestroyVoice();
Cleanup:
  return hr;
}

HRESULT RunFilePlayback()
{
  HRESULT hr = S_OK;
  mwrl::ComPtr<IXAudio2> xaudio;
  IXAudio2MasteringVoice* masteringVoice;

  const wchar_t WaveFileName[] = LR"(C:\nobackup\source\repos\directx-sdk-samples\Media\Wavs\MusicMono.wav)";

  IFC(XAudio2Create(xaudio.GetAddressOf(), 0, XAUDIO2_DEFAULT_PROCESSOR));
  IFC(xaudio->CreateMasteringVoice(&masteringVoice));
  IFC(PlayWave(xaudio.Get(), WaveFileName));

  masteringVoice->DestroyVoice();
  xaudio.Reset();

Cleanup:
  return hr;
}

int main()
{
  HRESULT hr = S_OK;

  IFC(CoInitializeEx(nullptr, COINIT_MULTITHREADED));
  IFC(RunFilePlayback());
  CoUninitialize();

Cleanup:
  return FAILED(hr) ? 1 : 0;
}


To build, run these commands. You'll really want Visual Studio installed with the C++ workload to get the right SDK headers, librarie and tools.

; open Native Command Tools for x64
mkdir C:\nobackup\scratchopus
cd C:\nobackup\scratchopus
; copy over WAVFileReader.cpp and WAVFileReader.h
cl play.cpp WAVFileReader.cpp /Fe: play.exe /link ole32.lib user32.lib && play.exe


Where do we get some data?

For the starting case, I'm using the sample wave file from Media/Wavs/MusicMono.wav.

Next time, we actually put the thing to use.

Happy sound playback!

Tags:  audio cpp

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