eg-sampler: Convert multi-channel audio files to mono

1 files changed, 25 insertions, 4 deletions

diff --git a/plugins/eg-sampler.lv2/sampler.c b/plugins/eg-sampler.lv2/sampler.c
index 779dc05..a3ef5c3 100644
--- a/plugins/eg-sampler.lv2/sampler.c
+++ b/plugins/eg-sampler.lv2/sampler.c
@@ -96,6 +96,23 @@ typedef struct {
 } SampleMessage;
 
 /**
+   Convert an interleaved audio buffer to mono.
+
+   This simply ignores the data on all channels but the first.
+*/
+static sf_count_t
+convert_to_mono(float* data, sf_count_t num_input_frames, uint32_t channels)
+{
+  sf_count_t num_output_frames = 0;
+
+  for (sf_count_t i = 0; i < num_input_frames * channels; i += channels) {
+    data[num_output_frames++] = data[i];
+  }
+
+  return num_output_frames;
+}
+
+/**
    Load a new sample and return it.
 
    Since this is of course not a real-time safe action, this is called in the
@@ -115,9 +132,8 @@ load_sample(LV2_Log_Logger* logger, const char* path)
   bool           error    = true;
   if (!sndfile || !info->frames) {
     lv2_log_error(logger, "Failed to open %s\n", path);
-  } else if (info->channels != 1) {
-    lv2_log_error(logger, "%s has %d channels\n", path, info->channels);
-  } else if (!(data = (float*)malloc(sizeof(float) * info->frames))) {
+  } else if (!(data = (float*)malloc(sizeof(float) * info->frames *
+                                     info->channels))) {
     lv2_log_error(logger, "Failed to allocate memory for sample\n");
   } else {
     error = false;
@@ -131,9 +147,14 @@ load_sample(LV2_Log_Logger* logger, const char* path)
   }
 
   sf_seek(sndfile, 0ul, SEEK_SET);
-  sf_read_float(sndfile, data, info->frames);
+  sf_read_float(sndfile, data, info->frames * info->channels);
   sf_close(sndfile);
 
+  if (info->channels != 1) {
+    info->frames   = convert_to_mono(data, info->frames, info->channels);
+    info->channels = 1;
+  }
+
   // Fill sample struct and return it
   sample->data     = data;
   sample->path     = (char*)malloc(path_len + 1);