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PORecording an audio stream in C# from C++ ASIO library
 

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    <p>I need to find the best way to record an audio stream. I have already built the low level code in C++ and interfaced parts of it to C#.</p> <p>So i have a C++ callback that gives me an array of array of floats - the audio signal. At the moment, my C++ lib is recording the data straight to the file in the wav format and it just notify my C# app when it ends recording.</p> <p>But, I would like to have more interactivity on the UI side, like 'infinite' progress bar, amount of the data recorded, cancel button etc, and since it's gonna be a minute at worst, maybe it's better to keep it in memory. I know very little about .NET and C# memory management, so i don't know how to make it efficiently.</p> <p>Is there any fast resizable container in C#, where i could just put the data inside and later access it like an array?</p> <p>I also would like to build a waveform image off it. I already have those things done in C++, but somehow i don't like the idea to write too much messaging, transfer objects etc.</p> <p>So to put things together:</p> <ol> <li><p>I have C++ unmanaged callback that does some stuff and from within i'd like to call C# method once it has processed the data, the C prototype would be:</p> <p>void process(float **signal, int n); (usually [2][n] - for stereo)</p> <p>What would be C# equivalent and how do i call it from that C++ callback ?</p></li> <li><p>What is the best class to write continuous stream to (like mem.put(float[][] data, int size) ) and then read it as an array or with other easy way (to save a wav file from it for example or make a waveform bitmap)</p></li> <li><p>Is there going to be a significant performance loss if i do it in C#? (managed c++ wrapper calling c# function etc... and probably some DSP stuff) or i am just paranoid ? :)</p></li> </ol> <p>Cheers,</p> <p>pablox</p> <h2>My solution</h2> <p>Ok i solved it that way:</p> <p>In my C++ header file i got transfer structure:</p> <pre><code>public ref struct CVAudio { public: float *left; float *right; int length; }; </code></pre> <p>Then in managed C++ class i have declared:</p> <pre><code>delegate void GetAudioData([In, Out] CVAudio^ audio); </code></pre> <p>Then i can use it as an argument to the method that initialize audio:</p> <pre><code>void initializeSoundSystem(void *HWnd, GetAudioData ^audio); </code></pre> <p>That delegate has also a C prototype of </p> <pre><code>typedef void (CALLBACK *GETAUDIODATA)(CVAudio ^a); </code></pre> <p>Which is used in the internal C++ class as:</p> <pre><code>void initializeSoundSystem(HWND HWnd, GETAUDIODATA audio); </code></pre> <p>Then body of the first method is:</p> <pre><code>void VDAudio::initializeSoundSystem(void *HWnd, GetAudioData ^audio) { HWND h = (HWND) HWnd; acb = audio; pin_ptr&lt;GetAudioData ^&gt; tmp = &amp;audio; IntPtr ip = Marshal::GetFunctionPointerForDelegate(audio); GETAUDIODATA cb = static_cast&lt;GETAUDIODATA&gt;(ip.ToPointer()); audioObserver-&gt;initializeSoundSystem(h, cb); } </code></pre> <p>Body of audioObserver just stores that callback in the object and do some audio related things.</p> <p>Callback is then called in the processing method like that:</p> <pre><code> VDAudio^ a = gcnew VDAudio(); a-&gt;left = VHOST-&gt;Master-&gt;getSample()[0]; //returns left channel float* a-&gt;right = VHOST-&gt;Master-&gt;getSample()[1]; a-&gt;length = length; (*callback)(a); </code></pre> <p>And the body of C# delegate:</p> <pre><code>public void GetSamples(CVAudio audio) { unsafe { float* l = (float*)audio.left; float* r = (float*)audio.right; if (l != null) { SamplePack sample = new SamplePack(); sample.left = new float[audio.length]; sample.right = new float[audio.length]; IntPtr lptr = new IntPtr((void*)l); IntPtr rptr = new IntPtr((void*)r); Marshal.Copy(lptr, sample.left, 0, audio.length); Marshal.Copy(rptr, sample.right, 0, audio.length); this.Dispatcher.Invoke(new Action(delegate() { GetSamples(sample); })); } } } </code></pre> <p>So probably that's not a best code around - i have no idea. Only can say it works, doesn't seem to leak etc. :)</p>
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    1. COAn admirable effort but have you considered http://code.google.com/p/sharpdx/ ?
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    2. COi am not using directx, but ASIO. I have everything re sound coded, i am just concerned about recording. I don't want to use 3rd party libs. Thank you for reply anyway :)
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    3. CO@pablox, Just out of curiosity, what are you using to communicate with the ASIO driver? Your own DLL? As far as I know, the only library usable with .NET for ASIO is BASS.net (http://www.un4seen.com/).
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