feat(test_demo): Add beat_number column to fine-grained peak log

Adds beat_number as 4th column in fine-grained logging mode to enable
easy correlation between frame-level data and beat boundaries.

File format change:
- Before: frame_number clock_time raw_peak
- After:  frame_number clock_time raw_peak beat_number

Benefits:
- Correlate frame-level peaks with specific beats
- Filter or group data by beat in analysis scripts
- Easier comparison between beat-aligned and fine-grained logs
- Identify which frames belong to each beat interval

Example output:
  0 0.000000 0.850000 0
  1 0.016667 0.845231 0
  ...
  30 0.500000 0.720000 1
  31 0.516667 0.715234 1

This allows filtering like: awk '$4 == 0' peaks_fine.txt
to extract all frames from beat 0.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/test_demo.cc b/src/test_demo.cc
index 5f36e30..4d2d60b 100644
--- a/src/test_demo.cc
+++ b/src/test_demo.cc
@@ -141,7 +141,7 @@ int main(int argc, char** argv) {
       fprintf(peak_log, "# To plot with gnuplot:\n");
       fprintf(peak_log, "#   gnuplot -p -e \"set xlabel 'Time (s)'; set ylabel 'Peak'; plot '%s' using 2:3 with lines title 'Raw Peak'\"\n", log_peaks_file);
       if (log_peaks_fine) {
-        fprintf(peak_log, "# Columns: frame_number clock_time raw_peak\n");
+        fprintf(peak_log, "# Columns: frame_number clock_time raw_peak beat_number\n");
       } else {
         fprintf(peak_log, "# Columns: beat_number clock_time raw_peak\n");
       }
@@ -193,7 +193,7 @@ int main(int argc, char** argv) {
     if (peak_log) {
       if (log_peaks_fine) {
         // Log every frame for fine-grained analysis
-        fprintf(peak_log, "%d %.6f %.6f\n", frame_number, current_time, raw_peak);
+        fprintf(peak_log, "%d %.6f %.6f %d\n", frame_number, current_time, raw_peak, beat_number);
       } else if (beat_number != last_beat_logged) {
         // Log only at beat boundaries
         fprintf(peak_log, "%d %.6f %.6f\n", beat_number, current_time, raw_peak);