Updates

Makefile

@@ -1,4 +1,7 @@
+-include .config
+
 CFLAGS += -Wall -MMD
+LDLIBS += -lm
 
 tempo:	tempo.o
 

tempo.c

@@ -1,7 +1,13 @@
 #include <assert.h>
 #include <math.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+#define BANNER "tempo 0.1 (C) Copyright 2011 Mark Hills <mark@pogo.org.uk>"
+#define NAME "tempo"
 
 #define RATE 44100 /* of input data */
 
@@ -13,27 +19,21 @@
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
 
 /*
- * Sample from the metered energy with interpolation
+ * Sample from the metered energy
+ *
+ * No need to interpolate and it makes a tiny amount of difference; we
+ * take a random sample of samples, any errors are averaged out.
  */
 
 static double sample(float nrg[], size_t len, double offset)
 {
-	double f, a, b;
-	size_t n;
+	double n;
+	size_t i;
 
-	n = (size_t)offset;
+	n = floor(offset);
+	i = (size_t)n;
 
-	f = offset - n;
-	if (f == 0.0)
-		return (n < len) ? nrg[n] : 0.0;
-
-	/* Linear interpolation */
-
-	a = (n < len) ? nrg[n] : 0.0;
-	n++;
-	b = (n < len) ? nrg[n] : 0.0;
-
-	return (1.0 - f) * a + f * b;
+	return (n >= 0.0 && n < (double)len) ? nrg[i] : 0.0;
 }
 
 /*
@@ -43,22 +43,28 @@ static double sample(float nrg[], size_t len, double offset)
 double autodifference(float nrg[], size_t len, double interval)
 {
 	size_t n;
-	double mid, v, diff = 0.0;
-	static const int beats[] = { -32, -16, -8, -4, -4, -4, -2, -2, -1,
-				     1, 2, 2, 4, 4, 4, 8, 16, 32 };
+	double mid, v, diff;
+	static const double beats[] = { -32, -16, -8, -4, -2, -1, 1, 2, 4, 8, 16, 32 },
+			nobeats[] = { -0.5, -0.25, 0.25, 0.5 };
 
 	mid = drand() * len;
 	v = sample(nrg, len, mid);
 
+	diff = 0.0;
 	for (n = 0; n < ARRAY_SIZE(beats); n++) {
-		int beat;
 		double y;
 
-		beat = beats[n];
-		y = sample(nrg, len, mid + beat * interval);
+		y = sample(nrg, len, mid + beats[n] * interval);
 		diff += fabs(y - v);
 	}
 
+	for (n = 0; n < ARRAY_SIZE(nobeats); n++) {
+		double y;
+
+		y = sample(nrg, len, mid + nobeats[n] * interval);
+		diff -= fabs(y - v);
+	}
+
 	return diff;
 }
 
@@ -96,7 +102,8 @@ double interval_to_bpm(double interval)
 double scan_for_bpm(float nrg[], size_t len,
 		double slowest, double fastest,
 		unsigned int steps,
-		unsigned int samples)
+		unsigned int samples,
+		bool graph)
 {
 	double step, interval, trough, height;
 	unsigned int s;
@@ -107,17 +114,16 @@ double scan_for_bpm(float nrg[], size_t len,
 
 	height = INFINITY;
 
-	for (;;) {
+	for (interval = fastest; interval <= slowest; interval += step) {
 		double t;
 
-		interval += step;
-		if (interval > slowest)
-			break;
-
 		t = 0.0;
 		for (s = 0; s < samples; s++)
 			t += autodifference(nrg, len, interval);
 
+		if (graph)
+			printf("%lf\t%lf\n", interval_to_bpm(interval), t);
+
 		/* Track the lowest value */
 
 		if (t < height) {
@@ -129,13 +135,70 @@ double scan_for_bpm(float nrg[], size_t len,
 	return interval_to_bpm(trough - (step / 2));
 }
 
+void usage(FILE *f)
+{
+	fprintf(f, "Usage: " NAME " [options]\n"
+		"Analyse the tempo (in beats-per-minute, BPM) of incoming audio\n\n"
+		"  -g   Output autodifference graph to stdout\n"
+		"  -f   Print format for final BPM value (default \"%%0.1f\")\n"
+		"  -v   Print progress information to stderr\n"
+		"  -h   Display this help message and exit\n\n");
+
+	fprintf(f, "Incoming audio is raw audio at %dHz, mono, 32-bit float; eg.\n"
+		"  sox file.mp3 -t raw -r %d -e float -c 1 | ./" NAME "\n",
+		RATE, RATE);
+}
+
 int main(int argc, char *argv[])
 {
 	float *nrg = NULL;
 	size_t len = 0, buf = 0;
 	off_t n = 0;
-	double bpm;
-	float v = 0.0;
+	float bpm, v = 0.0;
+	const char *format = "%0.1f";
+	bool verbose = false;
+
+	for (;;) {
+		int c;
+
+		c = getopt(argc, argv, "vf:gh");
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'v':
+			verbose = true;
+			break;
+
+		case 'f':
+			format = optarg;
+			break;
+
+		case 'g':
+			format = NULL;
+			break;
+
+		case 'h':
+			usage(stdout);
+			return 0;
+
+		default:
+			return EX_USAGE;
+		}
+	}
+
+	argv += optind;
+	argc -= optind;
+
+	if (argc > 0) {
+		fprintf(stderr, "%s: Too many arguments\n", NAME);
+		return EX_USAGE;
+	}
+
+	if (verbose) {
+		fputs(BANNER "\n", stderr);
+		fprintf(stderr, "Metering incoming audio\n");
+	}
 
 	for (;;) {
 		float z;
@@ -164,21 +227,32 @@ int main(int argc, char *argv[])
 		if (len == buf) {
 			size_t n;
 
-			fprintf(stderr, "Reallocating at %zd\n", len);
-
 			n = buf + BLOCK;
 			nrg = realloc(nrg, n * sizeof(*nrg));
-			assert(nrg != NULL);
+			if (nrg == NULL) {
+				perror("realloc");
+				return -1;
+			}
 			buf = n;
 		}
 
 		nrg[len++] = v;
 	}
 
-	bpm = scan_for_bpm(nrg, len, 60.0, 180.0, 400, 1000);
-	printf("BPM = %f\n", bpm);
+	if (verbose)
+		fprintf(stderr, "Sampling tempo range\n");
+
+	bpm = scan_for_bpm(nrg, len, 60.0, 180.0, 400, 1000, (format == NULL));
+
+	if (format != NULL) {
+		printf(format, bpm);
+		putc('\n', stdout);
+	}
 
 	free(nrg);
 
+	if (verbose)
+		fprintf(stderr, "Done\n");
+
 	return 0;
 }