Accessing Raw Amplitude Data from imported WAV file

[hiraz01]

How does one retrieve the raw amplitude data from a file? I went through the documentation and got the simple_playback.c and simple_capture.c working, but I can't seem to figure out how to copy over the raw data to the main program and use it. I tried to cast the device pUserData to a float* but I am a bit lost. I ultimately want to play sound while keeping track of amplitude in real time. In the AudioFile library we can do something like,
int channel = 0;
int numSamples = audioFile.getNumSamplesPerChannel();
for (int i = 0; i < numSamples; i++)
double currentSample = audioFile.samples[channel][i];
Any help would be greatly appreciated.

[mackron]

In the simple_playback example you'll see how there's a call to ma_decoder_read_pcm_frames(). You would use that. In the example it's outputting straight to the callback's output buffer, but instead you would just output it to your own buffer and do whatever it is you need to do. Just make sure that you copy the data over to the callback's output buffer eventually or else you won't hear anything. If you need your samples in floating point format, make sure you configure the decoder to output samples as ma_format_f32:

ma_decoder_config decoderConfig = ma_decoder_config_init(ma_format_f32, channels, sampleRate);

[mackron]

So the decoder (ma_decoder) and the device (ma_device) are 100% decoupled from each other. You can call ma_decoder_read_pcm_frames() wherever you want, so long as at some point you give the device some data when it asks for it (when the data callback is called). Thinking of the two as decoupled might help you wrap your head around it. The data callback is just asking for some audio data. It doesn't care where you get it from, just so long as you give it something (if you don't you'll get glitching). It just so happens that in the simple_playback example we're getting from a file that we've loaded from the file system and have decoded via ma_decoder. It doesn't have to come from a decoder. You could use ma_waveform to give it a sine wave if you wanted, or you could even pass in random junk if you wanted (not recommended!).

An easy solution for only loading the sound once is to load the raw file data into a heap-allocated buffer. Then use ma_decoder_init_memory() instead of ma_decoder_init_file(). Pass in a pointer to the buffer containing the raw file data and it's size in bytes. miniaudio will not make a copy of that data when you initialize a decoder which means each ma_decoder instantiation should be relatively lightweight. You can initialize many ma_decoder objects against that one buffer.

[hiraz01]

Progress has been made. Thank you very much. I was able to get the myBuffer to plot in ImGui while also using the same decoder initialized from the ma_decoder_init_file() to start and stop the device. Yesterdays issues were mostly to do with the cursor position of the decoder and my lack of understanding there.

Being able to load the sound once as described in your response sounds really great, but I ran into an issue trying to load the myBuffer generated from the ma_decoder_init_file. To simplify I tried to take it back to a basic case where I heap allocated a 3 element array with no luck either. I either get NOT MA_SUCCESS or a memcpy crash in the case of trying to initialize the myBuffer from the file init.
Simplest example I could come up with...
ma_decoder buffdecoder;
ma_result maResult2;
float* buffer = new float[3];
buffer[0] = 0.0500f;
buffer[1] = 0.0250f;
buffer[2] = 0.0125f;
maResult2 = ma_decoder_init_memory(buffer, 3 * sizeof(float), NULL, &buffdecoder);

I tried to setup the ma_decoder_config beforehand, but no luck their either. Thanks again for all your help.

[hiraz01]

By the way, I generate myBuffer like so:

myBuffer = (float*)malloc(readLength * 1 * sizeof(float));
ma_decoder_read_pcm_frames(&myDecoder, myBuffer, readLength, NULL);

[mackron]

That's not the correct usage of ma_decoder_init_memory(). You want to pass in the raw file data, not actual audio data. So the raw data of the MP3 file, or whatever file format you're using (miniaudio has built-in support for WAV, FLAC and MP3).

[hiraz01]

Alrighty. Thanks a lot for all your help! I will mark your previous response regarding ma_decoder_init_memory() as the answer. Cheers.