Don't write default values for fixed parameters

reaper-adm-extension/src/reaper_adm/exportaction_parameterprocessing.cpp

@@ -204,6 +204,12 @@ std::vector<AdmAuthoringError> CumulatedPointData::useConstantValueForParameter(
         errors.push_back(AdmAuthoringError("Attempting to assign a constant value to an ADM parameter which already has parameter data."));
         return errors;
     }
+    // If a parameter is constant and set to it's default, it doesn't need to be explicitly written, so just return
+    if (auto defaultValue = getAdmParameterDefault(admParameter);
+        defaultValue && valueWithinTolerance(value, *defaultValue)) {
+        return errors;
+    }
+    // Non-default, constant value parameter, so add a point
     // No need to convert/scale here - it's not from an envelope
     newPointData(0.0, admParameter, value);
     return errors;

reaper-adm-extension/src/reaper_adm/exportaction_pcmsink.cpp

@@ -105,7 +105,11 @@ PCM_sink_adm::PCM_sink_adm(std::shared_ptr<ReaperAPI> api, const char *fn, void
     // Start writing
     auto chna = admExportSources->getChnaChunk();
     auto axml = admExportSources->getAxmlChunk();
-    writer = bw64::writeFile(admFilename, totalChannels, sRate, 24, chna, axml);
+    try {
+        writer = bw64::writeFile(admFilename, totalChannels, sRate, 24, chna, axml);
+    } catch (std::runtime_error const& e) {
+        errors.push_back(std::string("Error: Unable to open output file for writing: ") + e.what());
+    }
 
     // Start Renders
     admExportSources->setRenderInProgress(true);
@@ -200,6 +204,9 @@ void PCM_sink_adm::WriteDoubles(double **samples, int len, int nch, int offset,
 }
 
 int PCM_sink_adm::processNextFrames(uint64_t toMaxFrame){
+    if (!writer) {
+        return 0;
+    }
 
     float *bufferWritePos = aggregatedBlockBufferStart;
     size_t sampleSize = sizeof(float);