This squashed commit comprises a long series of improvements, bug fixes, optimizations, and new feature additions:

- 48,000 frames per second operation,
 - 48k lossless stereo, 5.1 and 7.1 surround sound
 - Multichannel and multi rate operation on ALSA, PipeWire, PulseAudio, FreeBSD, stdout and unix pipe output backends.

Automatic, flexible and controllable output format (rate, sample format and channel count) selection.

Full FFmpeg integration to support transcoding, resampling, and new audio formats.

Better operation on lower powered devices down to e.g. Raspberry Pi B.

Reduced Docker image sizes with a slimmed-down FFmpeg library.

Enhanced timestamp handling for better synchronization.

Improved the sync error calculation.

A new "vernier" resampling and interpolation method for low-power CPUs.

Bug fixes and minor enhancements.

Note -- there are many breaking changes from previous versions of Shairport Sync!

dacp.c

@@ -1,6 +1,6 @@
 /*
  * DACP protocol handler. This file is part of Shairport Sync.
- * Copyright (c) Mike Brady 2017 -- 2020
+ * Copyright (c) Mike Brady 2017--2025
  * All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person
@@ -74,9 +74,22 @@ struct HttpResponse {
 };
 
 void *response_realloc(__attribute__((unused)) void *opaque, void *ptr, int size) {
-  void *t = realloc(ptr, size);
-  if ((t == NULL) && (size != 0))
-    debug(1, "Response realloc of size %d failed!", size);
+  void *t = NULL;
+  if (size == 0) {
+    // debug(1, "response_realloc of size 0 to ptr %" PRIxPTR " requested, and a pointer of NULL was
+    // returned.", size, ptr);
+    free(ptr);
+  } else {
+    if (ptr == NULL) {
+      t = malloc(size);
+      // debug(1, "response_realloc of size %d to a NULL pointer was requested, and a pointer of %"
+      // PRIxPTR " was returned.", size, t);
+    } else {
+      t = realloc(ptr, size);
+    }
+    if (t == NULL)
+      debug(1, "response_realloc of size %d to ptr %" PRIxPTR " failed!", size, ptr);
+  }
   return t;
 }
 
@@ -104,8 +117,7 @@ void response_body(void *opaque, const char *data, int size) {
 static void
 response_header(__attribute__((unused)) void *opaque, __attribute__((unused)) const char *ckey,
                 __attribute__((unused)) int nkey, __attribute__((unused)) const char *cvalue,
-                __attribute__((unused)) int nvalue) { /* example doesn't care about headers */
-}
+                __attribute__((unused)) int nvalue) { /* example doesn't care about headers */ }
 
 static void response_code(void *opaque, int code) {
   struct HttpResponse *response = (struct HttpResponse *)opaque;
@@ -255,7 +267,7 @@ int dacp_send_command(const char *command, char **body, ssize_t *bodysize) {
             ssize_t wresp = send(sockfd, message, strlen(message), 0);
             if (wresp == -1) {
               char errorstring[1024];
-              strerror_r(errno, (char *)errorstring, sizeof(errorstring));
+              getErrorText((char *)errorstring, sizeof(errorstring));
               debug(2, "dacp_send_command: write error %d: \"%s\".", errno, (char *)errorstring);
               struct linger so_linger;
               so_linger.l_onoff = 1; // "true"
@@ -272,7 +284,7 @@ int dacp_send_command(const char *command, char **body, ssize_t *bodysize) {
 
               response.body = malloc(2048); // it can resize this if necessary
               response.malloced_size = 2048;
-              pthread_cleanup_push(malloc_cleanup, response.body);
+              pthread_cleanup_push(malloc_cleanup, &response.body);
 
               struct http_roundtripper rt;
               http_init(&rt, responseFuncs, &response);
@@ -291,9 +303,11 @@ int dacp_send_command(const char *command, char **body, ssize_t *bodysize) {
                 if (ndata <= 0) {
                   if (ndata == -1) {
                     char errorstring[1024];
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-result"
                     strerror_r(errno, (char *)errorstring, sizeof(errorstring));
-                    debug(2, "dacp_send_command: receiving error %d: \"%s\".", errno,
-                          (char *)errorstring);
+#pragma GCC diagnostic pop
+                    debug(2, "dacp_send_command: receiving error %d: \"%s\".", errno, errorstring);
                     struct linger so_linger;
                     so_linger.l_onoff = 1; // "true"
                     so_linger.l_linger = 0;
@@ -461,7 +475,7 @@ void set_dacp_server_information(rtsp_conn_info *conn) {
 
 void dacp_monitor_port_update_callback(char *dacp_id, uint16_t port) {
   debug_mutex_lock(&dacp_server_information_lock, 500000, 2);
-  debug(2,
+  debug(3,
         "dacp_monitor_port_update_callback with Remote ID \"%s\", target ID \"%s\" and port "
         "number %d.",
         dacp_id, dacp_server.dacp_id, port);
@@ -489,6 +503,8 @@ void dacp_monitor_port_update_callback(char *dacp_id, uint16_t port) {
 }
 
 void *dacp_monitor_thread_code(__attribute__((unused)) void *na) {
+  //  #include <syscall.h>
+  //  debug(1, "dacp_monitor_thread_code PID %d", syscall(SYS_gettid));
   int scan_index = 0;
   int always_use_revision_number_1 = 0;
   // char server_reply[10000];
@@ -982,7 +998,7 @@ void dacp_monitor_start() {
 
   memset(&dacp_server, 0, sizeof(dacp_server_record));
 
-  pthread_create(&dacp_monitor_thread, NULL, dacp_monitor_thread_code, NULL);
+  named_pthread_create(&dacp_monitor_thread, NULL, dacp_monitor_thread_code, NULL, "dacp");
   dacp_monitor_initialised = 1;
 }