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!

rtsp.h

@@ -26,6 +26,16 @@ void metadata_stop(void);
 // e.g. if it's malloced, to free it, etc.
 // nothing is done automatically
 
-int send_ssnc_metadata(uint32_t code, char *data, uint32_t length, int block);
+int send_ssnc_metadata(const uint32_t code, const char *data, const uint32_t length,
+                       const int block);
+
+#ifdef CONFIG_AIRPLAY_2
+ssize_t read_encrypted(int fd, pair_cipher_bundle *ctx, void *buf, size_t count);
+ssize_t write_encrypted(int fd, pair_cipher_bundle *ctx, const void *buf, size_t count);
+
+void generateTxtDataValueInfo(rtsp_conn_info *conn, void **response, size_t *responseLength);
+plist_t generateInfoPlist(rtsp_conn_info *conn);
+char *plist_as_xml_text(plist_t the_plist); // caller must free the returned NUL-terminated string
+#endif
 
 #endif // _RTSP_H