From e7f3e475a26b7a2aff38e2b97fdeee793f647871 Mon Sep 17 00:00:00 2001
From: ed <s@ocv.me>
Date: Fri, 31 Mar 2023 21:20:37 +0000
Subject: [PATCH] more accurate bpm detector

---
 bin/mtag/audio-bpm.py | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/bin/mtag/audio-bpm.py b/bin/mtag/audio-bpm.py
index c9abec95..d7f2c1c5 100755
--- a/bin/mtag/audio-bpm.py
+++ b/bin/mtag/audio-bpm.py
@@ -16,6 +16,10 @@ dep: ffmpeg
 """
 
 
+# save beat timestamps to ".beats/filename.txt"
+SAVE = False
+
+
 def det(tf):
     # fmt: off
     sp.check_call([
@@ -23,12 +27,11 @@ def det(tf):
         b"-nostdin",
         b"-hide_banner",
         b"-v", b"fatal",
-        b"-ss", b"13",
         b"-y", b"-i", fsenc(sys.argv[1]),
         b"-map", b"0:a:0",
         b"-ac", b"1",
         b"-ar", b"22050",
-        b"-t", b"300",
+        b"-t", b"360",
         b"-f", b"f32le",
         fsenc(tf)
     ])
@@ -47,10 +50,29 @@ def det(tf):
             print(c["list"][0]["label"].split(" ")[0])
             return
 
-        # throws if detection failed:
-        bpm = float(cl[-1]["timestamp"] - cl[1]["timestamp"])
-        bpm = round(60 * ((len(cl) - 1) / bpm), 2)
-        print(f"{bpm:.2f}")
+    # throws if detection failed:
+    beats = [float(x["timestamp"]) for x in cl]
+    bds = [b - a for a, b in zip(beats, beats[1:])]
+    bds.sort()
+    n0 = int(len(bds) * 0.2)
+    n1 = int(len(bds) * 0.75) + 1
+    bds = bds[n0:n1]
+    bpm = sum(bds)
+    bpm = round(60 * (len(bds) / bpm), 2)
+    print(f"{bpm:.2f}")
+
+    if SAVE:
+        fdir, fname = os.path.split(sys.argv[1])
+        bdir = os.path.join(fdir, ".beats")
+        try:
+            os.mkdir(fsenc(bdir))
+        except:
+            pass
+
+        fp = os.path.join(bdir, fname) + ".txt"
+        with open(fsenc(fp), "wb") as f:
+            txt = "\n".join([f"{x:.2f}" for x in beats])
+            f.write(txt.encode("utf-8"))
 
 
 def main():