diff --git a/generate-test-data.py b/generate-test-data.py
index e29b00b..559ef5f 100644
--- a/generate-test-data.py
+++ b/generate-test-data.py
@@ -1,9 +1,16 @@
 from datetime import datetime, timedelta
+import subprocess
 
 KBITS = 128
 
 
-bytes_per_second = KBITS * 1000 // 8
+def generate_test_file(fn, delta):
+    subprocess.call(['ffmpeg',
+                     '-f', 'lavfi',
+                     '-i', 'sine=frequency=1000:duration=%d' % delta.total_seconds(),
+                     '-b:a', '%dk' % KBITS,
+                     fn])
+
 
 start = datetime.now().replace(minute=0, second=0) - timedelta(hours=3)
 end = start + timedelta(hours=6)
@@ -14,8 +21,6 @@ while t < end:
     fn = 'tmp/qfhi-{:04d}{:02d}{:02d}-{:02d}{:02d}.mp3'.format(
             t.year, t.month, t.day, t.hour, t.minute)
     print(fn)
-    f = open(fn, 'w')
-    f.write('\0' * (int(delta.total_seconds()) * bytes_per_second))
-    f.close()
+    generate_test_file(fn, delta)
 
     t += delta