--- a/.hgignore	Wed May 15 02:31:01 2024 +0000
+++ b/.hgignore	Wed May 15 02:50:50 2024 +0000
@@ -15,3 +15,4 @@
 ^pcap-study/rtp-tfo-trace$
 
 ^pcm-study/g711u-grep-gsmout$
+^pcm-study/pcm-frag-extr$

--- a/pcm-study/Makefile	Wed May 15 02:31:01 2024 +0000
+++ b/pcm-study/Makefile	Wed May 15 02:50:50 2024 +0000
@@ -1,4 +1,4 @@
-PROGS=	g711u-grep-gsmout
+PROGS=	g711u-grep-gsmout pcm-frag-extr
 
 include ../config.defs
 
@@ -7,6 +7,9 @@
 g711u-grep-gsmout:	g711u-grep-gsmout.c
 	${CC} ${CFLAGS} -o $@ $@.c
 
+pcm-frag-extr:	pcm-frag-extr.c
+	${CC} ${CFLAGS} -o $@ $@.c
+
 install:
 	mkdir -p ${DESTDIR}${bindir}
 	install -c ${PROGS} ${DESTDIR}${bindir}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pcm-study/pcm-frag-extr.c	Wed May 15 02:50:50 2024 +0000
@@ -0,0 +1,50 @@
+/*
+ * This program extracts a fragment of some N 160-sample frames from a G.711
+ * recording file, starting at an arbitrary offset that may not be frame-
+ * aligned, and saves this fragment to a new binary file.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+main(argc, argv)
+	char **argv;
+{
+	FILE *inf, *outf;
+	u_long start_offset;
+	unsigned n, nframes;
+	uint8_t buf[160];
+	int cc;
+
+	if (argc != 5) {
+		fprintf(stderr,
+		"usage: %s pcm-src-file start-offset N-frames pcm-out-file\n",
+			argv[0]);
+		exit(1);
+	}
+	inf = fopen(argv[1], "r");
+	if (!inf) {
+		perror(argv[1]);
+		exit(1);
+	}
+	start_offset = strtoul(argv[2], 0, 0);
+	fseek(inf, start_offset, SEEK_SET);
+	nframes = strtoul(argv[3], 0, 0);
+	outf = fopen(argv[4], "w");
+	if (!outf) {
+		perror(argv[4]);
+		exit(1);
+	}
+	for (n = 0; n < nframes; n++) {
+		cc = fread(buf, 1, 160, inf);
+		if (cc > 0)
+			fwrite(buf, 1, cc, outf);
+		if (cc < 160) {
+			fprintf(stderr, "warning: short read from %s\n",
+				argv[1]);
+			break;
+		}
+	}
+	exit(0);
+}