changed the way we're looping over the samples. We're now looking onl…

…y once at each input sample. we're not seeking in the input file. This is required for reading from stdin to work. A small drawback is, that we have to collect all output values in a vector before output.

src/main.cpp

@@ -71,27 +71,16 @@ int main(int argc, char* argv[])
       return 2;
   }
 
-  for(size_t i = 0; i != options.channels.size(); ++i)
-  {
-    wav.seek(0, SEEK_SET);
-
-    Options::Channel channel = options.channels[i];
-
-    ofs << "  \"" << channel << "\":";
-
-    compute_waveform(
-      wav,
-      ofs,
-      options.samples,
-      channel,
-      options.use_db_scale,
-      options.db_min,
-      options.db_max,
-      progress_callback
-    );
-
-	  ofs << "," << std::endl;
-  }
+  compute_waveform(
+    wav,
+    ofs,
+    options.samples,
+    options.channels,
+    options.use_db_scale,
+    options.db_min,
+    options.db_max,
+    progress_callback
+  );
 
   // increase precission for duration
   ofs << std::fixed; //explicitly use fixed notation

src/wav2json.cpp

@@ -84,15 +84,13 @@ void compute_waveform(
   const SndfileHandle& wav,
   std::ostream& output_stream,
   size_t samples,
-  Options::Channel channel,
+  Options::Channels channels,
   bool use_db_scale,
   float db_min,
   float db_max,
   progress_callback_t progress_callback
 )
 {
-  output_stream << "[";
-
   using std::size_t;
   using std::cerr;
   using std::endl;
@@ -113,20 +111,34 @@ void compute_waveform(
   // temp buffer for samples from audio file
   std::vector<sample_type> block(samples_per_pixel);
 
-  if (
-      (channel == Options::MID  ||
-       channel == Options::SIDE ||
-       channel == Options::RIGHT||
-       channel == Options::MIN  ||
-       channel == Options::MAX
-      ) &&
-      wav.channels() == 1
-  )
+  // filter out channels, that require more channels than the wav file has
+  channels.erase(
+      std::remove_if(channels.begin(), channels.end(), [&wav](Options::Channel channel){
+          if ((channel == Options::MID  ||
+               channel == Options::SIDE ||
+               channel == Options::RIGHT||
+               channel == Options::MIN  ||
+               channel == Options::MAX) &&
+               wav.channels() == 1
+          )
+          {
+            std::cerr << "Warning: your trying to generate output for channel '" << channel << "', but the input has only one channel. removing requested channel." << std::endl;
+            return true;
+          }
+          return false;
+      }),
+      channels.end()
+  );
+
+  if (channels.empty())
   {
-    std::cerr << "Warning: your trying to generate output for channel '" << channel << "', but the input has only one channel. falling back to the left channel." << std::endl;
-    channel = Options::LEFT;
+    std::cerr << "Warning: there are no channels left to process, aborting." << endl;
+    return;
   }
 
+  // create one vector of floats for each requested channel
+  std::vector<std::vector<float> > output_values( channels.size() );
+
   // https://github.com/beschulz/wav2json/pull/7
   // http://www.mega-nerd.com/libsndfile/api.html#note2
   const_cast<SndfileHandle&>(wav).command(SFC_SET_SCALE_FLOAT_INT_READ, 0, SF_TRUE);
@@ -138,38 +150,55 @@ void compute_waveform(
   */
   for (size_t x = 0; x < samples; ++x)
   {
-	  // read frames
+    // read frames
     sf_count_t n = const_cast<SndfileHandle&>(wav).readf(&block[0], frames_per_pixel) * wav.channels();
     assert(n <= (sf_count_t)block.size());
 
-    // find min and max
-    sample_type max(0);
-    for (int i=0; i<n; i+=wav.channels()) // only left channel
+    // for each requested channel
+    for(size_t channel_idx = 0; channel_idx != channels.size(); ++channel_idx)
     {
-      sample_type sample = compute_sample(block, i, wav.channels(), channel);
-      sample_type abs_sample = std::abs(sample);
-      max = std::max( max, abs_sample );
-    }
+      // find min and max
+      sample_type max(0);
+
+      Options::Channel channel = channels[channel_idx];
+      for (int i=0; i<n; i+=wav.channels()) // seek to next frame
+      {
+        sample_type sample = compute_sample(block, i, wav.channels(), channel);
+        sample_type abs_sample = std::abs(sample);
+        max = std::max( max, abs_sample );
+      }
+
+      float y = use_db_scale?
+              map2range( float2db(max / (float)sample_scale<sample_type>::value ), db_min, db_max, 0, 1):
+              map2range( max, 0, sample_scale<sample_type>::value, 0, 1);
+
+      // print progress
+      if ( x%(progress_divisor) == 0 )
+      {
+        if ( progress_callback && !progress_callback( 100*x/samples ) )
+          return;
+      }
 
-    float y = use_db_scale?
-      map2range( float2db(max / (float)sample_scale<sample_type>::value ), db_min, db_max, 0, 1):
-      map2range( max, 0, sample_scale<sample_type>::value, 0, 1);
+      output_values[channel_idx].push_back(y);
+    }
+  }
 
-    output_stream << y;
-    if (x != samples-1) //only write out comma, if this is not the last sample
-      output_stream << ",";
+  // finally output the collected values
+  for(size_t channel_idx = 0; channel_idx != channels.size(); ++channel_idx)
+  {
+    Options::Channel channel = channels[channel_idx];
 
-    // print progress
-    if ( x%(progress_divisor) == 0 )
+    output_stream << "  \"" << channel << "\": [";
+    for (size_t i = 0; i != output_values[channel_idx].size(); ++i)
     {
-      if ( progress_callback && !progress_callback( 100*x/samples ) )
-          return;
+      output_stream << output_values[channel_idx][i];
+      if (i != output_values[channel_idx].size()-1)
+        output_stream << ","; // only output comma, if not the last ellement
     }
+    output_stream << "]," << endl;
   }
-  
+
   // call the progress callback
   if ( progress_callback && !progress_callback( 100 ) )
     return;
-
-  output_stream << "]";
 }

src/wav2json.hpp

@@ -11,7 +11,7 @@ void compute_waveform(
   const SndfileHandle& wav,
   std::ostream& output_stream,
   size_t samples,
-  Options::Channel channel,
+  Options::Channels channels,
   bool use_db_scale,
   float db_min,
   float db_max,