Best Method to Encode Many Sounds to one WAV File

[cdigit]

I have a basic (awesome) multitrack recorder going where I can record from device input many ma_sound(s) and can play them back with sample accurate timing based on ma_engine time. I didn't consider how I would save all of these to disk while keeping the timing. Is it even possible? These are the thoughts in my head:

1. Encode in the callback function.
   Cons: Would work, but user has to playback everything to record.
2. The ma_sound(s) are backed by an underlying ma_node_graph; I would need to somehow get everything in the graph into a buffer without having to use an ma_device callback. If I can get a handle on an output buffer of the underlying ma_node_graph, then maybe I can make my own callback, which could just be a loop? Something like this?

ma_uint32 framesChunk = 512;
ma_uint32 startFrame = 0;
ma_uint32 endFrame = framesChunk;
 

// some buffer to put the output of the underlying `ma_node_graph` data in 
// (allocated and zeroed)
Buffer buffer;

while(endFrame < bufferSize)
{
  
   // read buffer at start and end frames and return a pointer to where to access the buffer 
   // next (pPCMFrames)
   pPCMFrames = readBuffer(&buffer, startFrame, endFrame);
    
   // populate the buffer with underlying node_graph data via engine
   ma_engine_read_pcm_frames(&g_engine, pPCMFrames, framesChunk);

   // encode and write the buffer, which should have data to disk
   ma_encoder_write_pcm_frames(&encoder, pPCMFrames, framesChunk);

   // increment the end frame index by framesChunk
   endFrame += framesChunk;

   // increment the start frame index by framesChunk
   startFrame + = framesChunk
}
ma_encoder_uninit(&encoder);

Can something like option 2 work? I'm thinking that if it made sense, it would loop much faster than the callback and be much quicker to encode.

[cdigit]

I've been working on implementing this and it's working to a degree. I mean I can hear the sounds and whatnot, but it's also loaded with static. I wonder if it has to do with the buffer not being setup properly. I'm going to continue to dig in and post some code, if I can't figure it out.

[cdigit]

I got it to work! I had the wrong format on the second ma_encoder that I used to write it to disk! I might be learning something after all! This is how I did it below.
Questions:

• I don't understand how pBufferRef3 is the correct channel count and format when I did not initialize it?
• How can I find out when to stop the loop instead of hardcoding an arbitrary value in the while condition?

void writeWav(){
    // logic to set the seek_to position and start & and times for all sounds to their recorded positions  
    // ...
    
    // todo: init the encoder before this function is called.
    ma_encoder encoder2;
    char * outputFile = "/Users/me/Documents/outall.wav";
    ma_encoder_config encoderConfig2 = ma_encoder_config_init(ma_encoding_format_wav, ma_format_f32, 2, 44100);
    if (ma_encoder_init_file(outputFile, &encoderConfig2, &encoder2) != MA_SUCCESS) {
        printf("Failed to initialize output file.\n");
    }
     
   // stop and reset engine
    ma_engine_set_time(&g_engine, 0);
    ma_engine_stop(&g_engine);

    ma_uint32 framesChunk = 512;
    ma_uint32 endFrame = framesChunk;
    
   // setup a buffer
    ma_audio_buffer_ref * pBufferRef3;
    pBufferRef3 = (ma_audio_buffer_ref *)malloc(sizeof(*pBufferRef3));
    
    // todo: ma_audio_buffer_ref_get_length_in_pcm_frames or something 
    while(endFrame < 400000){

          // populate the buffer with underlying node_graph data via engine
          ma_engine_read_pcm_frames(&g_engine, pBufferRef3, framesChunk, NULL);

          // encode and write the buffer, which should have data to disk
          ma_encoder_write_pcm_frames(&encoder2, pBufferRef3, framesChunk, NULL);

          // increment the end frame index by framesChunk
          endFrame += framesChunk;


       
    }
    ma_encoder_uninit(&encoder2);
    free(pBufferRef3);
}``

[cdigit]

How can I find out when to stop the loop instead of hardcoding an arbitrary value in the while condition?

I solved this by having a counter in the callback so that during the initial recording all frames are counted up, then when I am writing I have counter in the while loop so that it's:

while(true){
//...read frames
  if(framesWritten >= framesRecorded){
     break;
  }
}

Not sure if having a counter in the callback would cause a hit to low latency performance though.