Version 4.3 -- Security Updates, Bug Fixes and Enhancements

This update contains important security updates, bug fixes and enhancements. NQPTP must also be updated, and it should be updated before updating Shairport Sync. The Shared Memory Interface version of both Shairport Sync and NQPTP is now 10, i.e. smi10. Thus the version string of both apps should contain smi10:

$ nqptp -V
Version: 1.2.4. Shared Memory Interface Version: smi10.
$ shairport-sync -V
4.3-...-smi10-...

Notes

When updating NQPTP on Linux, be sure to remove the old service file as directed in the README.
Having completed both updates and installations, remember to restart NQPTP first and then restart Shairport Sync.

Security Updates

A crashing bug in NQPTP has been fixed.
The communications protocol used between NQPTP and Shairport Sync has been revised and made more resilient to attempted misuse.
In Linux systems, NQPTP no longer runs as root -- instead it runs as the restriced user nqptp, with access to ports 319 and 320 set by the installer via the setcap utility.

Enhancements

A new volume control profile called dasl-tapered has been added in which halving the volume control setting halves the output level. For example, moving the volume slider from full to half reduces the output level by 10dB, which roughly corresponds with a perceived halving of the audio volume level. Moving the volume slider from half to a quarter reduces the output level by a a further 10dB. The tapering rate is slightly modified at the lower end of the range if the device's attenuation range is restricted (less than about 55dB).

To activate the dasl-tapered profile, set the volume_control_profile to "dasl_tapered" in the configuration file and restart Shairport Sync.

Many thanks to David Leibovic, aka dasl-, for this.
On graceful shutdown, an active_end signal should now be generated if the system was in the active state. Addresses issue #1647. Thanks to Tucker Kern for raising the issue.

Bug Fixes

Fixed a bug that causes the Docker image to crash occasionally when OwnTone interrupted an existing iOS session. Thanks to aaronk6 for the report.
Fixed a cross-compliation error caused by not looking for the correct version of the ar tool. The fix was to substitute the correct version during the autoreconf phase. Thanks to sternenseemann for raising the issue and the PR containing the fix.
Updated the mDNS strings for the Classic AirPlay feature of AP2, so that it does not appear to provide MFi authentication. Addresses this discussion.
Always uses a revision number of 1 when looking for status updates on the DACP remote control port. This follows a suggestion in Issue #1658. Thanks to ejurgensen, as ever, for the report and the suggested fix.
Fixed a statistics bug (the minimum buffer size was incorrectly logged) and also tidy up the statistics logging interval logic for resetting min and max counters.
Added an important missing format string argument to a call in the Jack Audio backend. Many thanks to michieldwitte for their PR.

Maintenance

Stopped using a deprecated FFmpeg data structure reference.
Stopped using deprecated OpenSSL calls. Thanks to yubiuser for their PR -- which did some of the updating -- and for their guidance.
Run workflow-based tests on PRs automatically. Thanks to yubiuser for their PR.

Version 4.2

This release consists of enhancements and a number of important bug fixes to Version 4.1. For information on the new features of 4.1, including AirPlay 2 support, please see the section "Version 4.1" below.

If you are updating an existing installation of Shairport Sync, you must also update NQPTP. The reason is that this update to Shairport Sync requires NQPTP with Shared Memory Interface Version smi9 and will not work with older versions.

The Shared Memory Interface Version smi* needed by Shairport Sync is part of its version string, obtainable using $ shairport-sync -V.
You can check the Shared Memory Interface Version of the installed version of nqptp using $ nqptp -V.

Enhancements

Allow compilation with libplist version 2.3.0. Thanks to Markus Reiter.
Update GitHub Action Workflows -- many thanks to yubiuser.
Update MQTT documentation to correspond to updates in Home Assistant. Thanks to hunhejj.
Update NQPTP communication to improve performance. Shairport Sync now passes activity information to NQPTP, enabling it to process timing data more accurately.

Docker Image Enhancements

Add basic PulseAudio support. Thanks to Ferdynand Naczynski and thanks also to Noel Hibbard for championing this idea for a long time.
Update to Alpine 3.17 and ensure services such as Avahi and D-Bus start in the correct order. Thanks to yubiuser.

Bug Fixes

Sometimes the AirPlay Device ID generated by Shairport Sync was all zeros, and so was invalid, causing connectivity problems. The cause of the problem was that get_device_id was not interpreting getaddrinfo information correctly. Thanks to Carl Johnson for reporting the issue, finding the (rather obscure) cause of the problem and for providing code to fix it.
Fix a bug reported in Issue #1633. The bug was that when a Realtime Audio stream (e.g. playing from Spotify on iOS or using Shairport Sync as the Sound Output on a Mac) was played, it was fine, but when it was stopped and a second stream was started, the new stream could not be heard. The problem was that the PTP clock was not being correctly revalidated for second and subsequent Realtime Audio streams. The fix was to ensure that the PTP clock is revalidated on second and subsequent plays on the same connection. Thanks again to David Leibovic for finding the problem.
Use TCP keepalive a little more generally -- treat it the same as a client closing the link rather than just an error.
Remove three potential race conditions between Shairport Sync opening a TCP connection and the client checking that the connections are open. The problem was that the connections were being opened in threads that were created just before the client was given the connection information. If the threads were delayed (e.g. on a slow or busy processor), the client could use the connection information to check the connections, but find that they were not (yet) open. This could cause the client to terminate the session immediately with a TEARDOWN. The fix was to open the connections before creating those threads and before sending the connection information back to the client. In this way, the connections are guaranteed to be open before the client has the information it needs to try to open them, even if the threads ared delayed in starting. This bug would manifest itself by allowing play to proceed but not play anything.
When built for AirPlay 2, ensure the hexadecimal string that prefixes the AirPlay 1 Service Name in the Bonjour text strings matches the AirPlay 2 Device ID. For example, if the Service Name is Kitchen and the AirPlay 2 Device ID is b8:2f:eb:d7:85:df, the AirPlay 1 Service Name should be B82FEBD785DF@Kitchen. (When built for AirPlay 1, the hexadecimal prefix is simply a hash of the Service Name.) Thanks to Casper for raising the issue and to ejurgensen for identifying the cause of the problem.

Version 4.1.1

This release consists of enhancements and bug fixes to Version 4.1. For information on the new features of 4.1, including AirPlay 2 support, please see the section "Version 4.1" below.

Enhancement

Use the TCP keepalive facility to close a play session if the client connection drops for a minute.

Metadata Enhancements

Add FramePosition (phbt), FirstFramePosition (phb0), OutputRate (ofps), OutputFormat (ofmt), StreamType (styp), ServiceName (svna), ClientName (snam) properties to the D-Bus interface and to the metadata stream (codes in brackets).
FramePosition/FirstFramePosition metadata is generated only if the progress_interval in the metadata section of the configuration file is non-zero. The progress interval can also be set by a new SetFramePositionUpdateInterval method in the D-Bus interface.
FramePosition/FirstFramePosition metadata is of the form <RTP Frame number>/<Local Time> where the local time, in nanoseconds (a 64-bit number), is the precise time that frame should be played. The metadata is generated when the frame is placed in the output buffer, and is thus generated audio_backend_buffer_desired_length_in_seconds (usually 0.2 seconds) before the time in question.
Add xesam:albumArtist and xesam:composer metadata (if available) to the metadata bundle presented in the D-Bus interface.
Add a new metadata item: sps:songdatakind, derived from the asdk metadata token, to the metadata bundle presented in the D-Bus interface. If 0 it seems to indicate an item of a specific duration such as an audio track; if 1 it seems to mean the stream is of unknown duration, for example an internet radio stream.

Docker Enhancements

Launch the shairport-sync app as root user within the Docker container rather than as the user shairport-sync.
Add the configuration file and the sample configuration files back into the Docker image.

Bug Fixes

Fix a bug that prevented multiple classic AirPlay instances being recognised. The bug was that the 12-digit classic AirPlay service name prefixes for each instance were all identically derived from a MAC hardware address. The fix was to modify the generation of prefixes to depend on the service name as well as the hardware address.
Fix a bug that prevented play to the the PulseAudio backend from resuming after a pause. The bug was due to changes in the way pauses were handled and the fix was to reopen the stream if it is closed whenever a play or latency request was made.
Fix a long-standing bug which didn't close the socket used for the RTSP connection, potentially exhausting the sockets available.
Fix a bug in audio_alsa.c when there is no hardware device name.
Add a configuration check for the xxd program when building for AirPlay 2.
Fix a compilation bug on certain platforms by trying to use AC_CHECK_LIB to find libavcodec if the PKG_CHECK_MODULES check fails.

Documentation

Include and reference the HTML version of the man page.

Version 4.1

Really Big Update -- AirPlay 2!

Version 4.1 brings support for AirPlay 2 operation. It works with iOS, iPadOS, macOS, HomePod mini and Apple TV sources, but not with Windows. Limited support is available for HomeKit -- Shairport Sync speakers can be added to the Home app, though not all features are working. AirPlay 2 operation requires a companion program called NQPTP and requires a somewhat more powerful system. Please see AIRPLAY2.md for more.

Note that you can still build Shairport Sync to support "classic" AirPlay (aka "AirPlay 1") as before.

The various guides for building and updating Shairport Sync have been consolidated into BUILD.md.

Here is a brief list of the high-level new features and changes (more to be added):

AirPlay 2 operation.
Improved libao backend for better compatibility with HomeBrew installations.
Improved MQTT and D-Bus facilities.
Automatically-generated Docker images.

There have been many many bug fixes and enhancements to the core operation of Shairport Sync.

Version 3.3.9

Bug Fix

Version 3.3.9 fixes a build failure with convolution raised since automake 1.16.5 and https://git.savannah.gnu.org/cgit/automake.git/commit/?id=f4a3a70f69e1dbccb6578f39ef47835098a04624. Further details in Fabrice Fontaine's original PR to the development branch. Many thanks to Fabrice Fontaine for the bug report and for the fix.

Version 3.3.8

Enhancements

Documentation for the MQTT interface. Many thanks to minix1234!

Bug Fixes

Fix a bug in the alsa back end. In the interval between checking that the alsa device handle was non-NULL and actually using it, the handle could be set to NULL. The interval between check and usage is now protected.
Fix a bug in the alsa precision timing code. Thanks to durwin99, Nicolas Da Mutten, mistakenideas, Ben Willmore and giggywithit for the report.
Fix a bug that caused Shairport Sync to hang, but not actually crash, if an on-... script failed.
Fix a crash that occurred if metadata support is enabled during compilation but turned off in the configuration file. Thanks to Tim Curtis for the report.
Fix a crash that occurred playing from AirPower on Android. Thanks to Ircama for the report.
Fix the configure.ac file so that --without-<feature> configuration options are not interpreted as --with-<feature> options instead! Thanks to David Racine for the report.

Version 3.3.7

Docker Integration

Docker Hub integration. From now on, prebuilt Docker images should be available on the Docker Hub at https://hub.docker.com/r/mikebrady/shairport-sync.

New Feature

For the PulseAudio backend pa, added a new server entry to the pa section of the configuration file, allowing you to specify a connection to a remote or a local system PulseAudio instance instead of letting PulseAudio choose. Thanks to Guillaume Revaillot for this new feature.

Pesky Changes

The underlying timing system has been moved from 64-bit fixed-point time representation (like NTP) to a 64-bit unsigned nanoseconds representation. This should make precisely no difference to the functionality of Shairport Sync but the transition might inadvertently have introduced bugs. Problem reports gratefully received.

Bug Fixes

Fixed a number of bugs that prevented Shairport Sync from terminating cleanly in response to the MPRIS interface's Quit() command. Thanks to João Gabriel for reporting this issue.
Related to the above, the code used to terminate the application after a fatal error has been cleaned up. It now uses the correct exit() call rather than the rather hacky abort() call, returning the value of the constant EXIT_FAILURE (typically 1) to the caller .
Fixed a bug whereby the start and end of active mode tokens abeg and aend where not generated or published -- pend tokens were being generated instead. Thanks to minix1234 for the bug report and fix.
Fixed a bug calculating the instantaneous synchronisation error. This bug could occasionally cause Shairport Sync to lose synchronisation and maybe even to mute for a few seconds before resynchronising. It was caused doing modulo arithmetic incorrectly and it's been there for a while.
Removed a bug which would affect initial synchronisation if a FLUSH command was received from the player at an inopportune time.
Added code to do calculations involving the audio_backend_latency_offset_in_seconds and audio_backend_silent_lead_in_time settings correctly. Many thanks to Tucker Kern for discovering a number of bugs associated with this and for proposing a solution. This prompted a closer investigation and a number of further improvements were made, and a few "hostages to fortune" removed.
The DACP ID looks like a 64-bit number expressed in hexadecimal. It is normally quoted with leading zeroes removed, but in the _dacp._tcp service string, leading zeros are not removed from the DACP ID. The bug fix removes those leading zeroes. Thanks to julianc1969 for tracking down this bug so tenaciously!
Make the first output backend in the list of backends the default and make its name the default output_name.
Fix a flaw in resyncing -- a flush is set up but not triggered.
Ensure metadata and cover art are enabled if metadata support is included at compilation.
Set convolution defaults even if no configuration file is found.
Handle the active_remote_id token as a string rather than an unsigned 32-bit number -- it seems ROON uses a longer character sequence.

Enhancements

Added the strings -alac and -jack to the the version string returned by the -V command line option if Apple ALAC decoder support and Jack Audio support are included respectively.
Cleaned up and simplified the code that handles FLUSH requests coming from the player. (Debug messages are still a little verbose.)
Improved timing estimation. Shairport Sync has been using linear least-squares regression to estimate timing drift between the (remote) source clock and the local clock. This technique is now extended to provide an estimate of the remote-to-local clock difference itself. (The remote-to-local clock difference is used to remap the timing of audio frames from the remote device's clock to the local clock.)

Timing drift estimates are now saved when a sessions ends, keyed to the client IP number. When a new session starts from that IP number, the stored estimate is used until a new estimate can be generated from the new session.

In practice, the timing techniques in use up to now have been very accurate, but this should result in slightly smoother rates of correction.
Tidied up the creation and initial opening of pipes. Suppress repeated pipe-opening error messages.
Tidied up warnings and fatal error messages when log verbosity is zero.
Cleaned up the code that provides a silent lead-in to play on a back end without synchronisation, e.g. a pipe or stdout.
Added in commented-out code to check the timeliness of the release of audio to a back end without synchronisation, e.g. a pipe or stdout. TL;DR – so long as the back end does not block, frames will be released to it not more than one packet (352 frames) late.
Logs and statistics can now be directed to the system log (default), stdout, stderr or to a file or pipe of your choice using a new setting, log_output_to in the diagnostics section of the configuration file. This is very useful when the system log is disabled or diverted.
Audio data from the pipe back end and metadata from the metadata pipe are now written using standard blocking write commands rather than a slightly complex non-blocking write function. Pipes are now opened in non-blocking mode and changed to blocking mode when successfully opened.
Add a default name for the pipe backend: /tmp/shairport-sync-audio.
Separate threads are now used for each metadata subsystem. Until now, all metadata was processed on a single thread. This included writing to the metadata pipe and the multicast stream and supplying metadata for the mqtt interface and for the dbus and MPRIS interfaces. Unfortunately, that meant that a problem with any one of these subsystems could propagate into the others. Now they all run on separate threads. If one thread blocks, it will not interfere with the other subsystems.
Cleaned up and improved the code to synchronise the first frame of audio. This should result in more accurate and reliable initial synchronisation, usually to under a millisecond, and often to within 20 or 30 microseconds. Syncronisation should improve even when the silent lead-in time is as short as 0.3 seconds or when the audio_backend_latency_offset_in_seconds is as much as -1.7 seconds, i.e. when only 0.3 seconds of latency are left when the latency would normally be 2.0 seconds.
Cleaned up some confused uses of modulo arithmetic.
Cleaned up the allocation of memory for gathering running statistics – the heap is now used instead of the stack.
Cleaned up the display of statistics for backends that do not implement active synchronisation, e.g. the pipe and STDOUT back ends.
Cleaned up the audio_backend_silent_lead_in_time setting by adding an "auto" setting.
Improved synchronisation accuracy with short silence lead-ins.
While a player is active, the DACP port number to which to send remote commands should be broadcast over ZEROCONF/Bonjour. However, if that information is not available, Shairport Sync will now check for it every two seconds.
The timing software in the sndio backend does some extra sanity checking on certain time estimates, it may help a little when running on virtual machines.
Open metadata and audio pipes with 666 permissions to allow them to be shared by other applications.

Version 3.3.6

New Features

Resampling has been added for the Jack Audio backend. This can be used to up-sample to 192kHz. Thanks to Pieter De Gendt for this addition.

Enhancements

Add SetAirplayVolume to the native D-Bus RemoteControl interface.
Add SetVolume to the MPRIS interface.
Add a few sample commands, including MPRIS commands, to the Sample D-Bus Commands document.

Bug Fixes

Add a SIGCHLD handler to remove completed processes that were used to perform program "hooks" without waiting for completion and thus prevent them from becoming zombie processes. Thanks to patrickjane for reporting the bug and for suggesting a solution. Addresses issue #968.
Fix a bug in the provision of metadata which would on occasion cause metadata from the previous track to be provided. Thanks to Tuomas Hämäläinen and HiFiBerry for reporting. This bugfix addresses issue #972.
Make Shairport Sync compile in the forthcoming Fedora 32. Fedora 32 uses GCC-10 which defaults to -fno-common exposing a number of issues with Shairport Sync – multiple definitions of some enums and failure to define certain variables as extern. Many thanks to Bill Peck for bringing this issue to notice. Address issue #973.
Treat the mper (Persistent ID of a track) metadata attribute as the 64-bit item that it really is rather than a 32-bit item as hithereto. Output it as a hexadecimal number on the MPRIS and D-Bus interfaces to correspond with the format of the persistent id obtained from AppleScript. Thanks to to Scott Simon (https://github.com/zutroy97) for finding a related bug in the shairport-sync-metadata-reader.
Hook up the Volume property in the MPRIS interface.
Fix an incompatibilty with Forked Daapd that was causing Forked Daapd to lock up. Thanks to @tomgadow and @ejurgensen for their help in finding and (hopefully) fixing this issue. Addresses issue #953 and Forked Daapd Issue #870.
Other minor bug fixes.

Pesky Changes You Might Not Be Able To Ignore

Renamed the Server property in the D-Bus interface to Client. The rather strange language in use has it that a player like iTunes is a "client" of the AirPlay device like Shairport Sync, which is therefore considered the "server". The newly-renamed "Client" property is the IP number of the player.

Version 3.3.5

Bug Fixes

Fix a crashing bug if output format S24 was chosen. Thanks to artenverho for reporting. Fixes Issue #927.
Fix a bug whereby if Loudness was enabled through the D-Bus interface, the output would be muted until the volume was changed.

Enhancements

D-Bus interface enhancements: add Convolution, ConvolutionGain and ConvolutionImpulseResponseFile properties to the D-Bus interface. These properties can be set and changed at any time, even while playing. Implements the suggestion in Issue #929. Thanks to corrpel for the suggestion.
Update the sample dbus commands document.

Pesky Changes

D-Bus interface change: the D-Bus LoudnessFilterActive property has been changed to Loudness. The sample D-Bus client has been updated accordingly.

Version 3.3.4

This is Version 3.3.3 with a small compilation error fixed.

Version 3.3.3

Bug Fixes

Fixes a deferred crash that occurred in Ubuntu 14.04: the shairport-sync daemon would silently die after a fairly long period. It typically happened just after a DHCP address was renewed. The problem seemed to be related to having more than one avahi threaded polling loop (though this isn't documented anywhere). The fix was to consolidate the avahi stuff down to one threaded polling loop. Addresses issue #895. Thanks to Hans (the) MCUdude for reporting and for initial troubleshooting.
Fixes a potential crash when an incomplete fmtp parameter set is sent by the requesting client. Thanks to Angus71 for the fault report and for the repair.
Fixed a potential crash -- if a plain HTTP packet (in fact, any packet that didn't have an RTSP-style header) was sent to the TCP session port (usually port 5000), Shairport Sync would crash! Thanks to @dubo-dubon-duponey for reporting. Fixes #921.
A fix ensures the hardware mixer of an alsa device is detected and initialised before responding to the first volume setting.
Fixes were made to the MPRIS and native D-Bus interfaces. In particular, situations where artwork is absent are better handled, and the remote interface and advanced remote interface availability properties should be more resilient in the face of network problems. Addresses issue #890. Improvements were made to the detection of the remote services available when an audio source is playing. If the source is minimally compatible, e.g. iOS, Shairport Sync's org.gnome.ShairportSync.RemoteControl native dbus interface becomes "available". If the source is iTunes, then the org.gnome.ShairportSync.AdvancedRemoteControl interface also becomes available. Artwork, metadata, status and limited remote control facilities are accessible through these interfaces when they are in the available state. Thanks to exoqrtx for bringing these issues to light and for testing.
Fixes an error whereby the 'pvol'volume metadata was no longer sent if Shairport Sync was configured to ignore volume control information coming from the audio source. Addresses issue #903. Thanks to Jordan Bass for reporting the regression and for identifying the commit and code in which the regression occurred.

Enhancements

Instead of returning EXIT_FAILURE, return EXIT_WITH_SUCCESS on early exit with either "version" (–version or -V) or "help" (–help or -h) arguments. Thanks to Henrik Nilsson for the patch.
Normalises the 'pvol' volume outputs so that when both the software and hardware attenuators are in use to extend the overall attenuation range, the maximum output level corresponds to the maximum output level of the hardware mixer.
Add the option of including the file and line number of each log entry's source. The option is on by default and is settable in the configuration file and in the dbus interface.
Rewrite the logic for identifying missing packets of audio and for asking for resends. It seems more robust -- there was a suspicion of the previous logic that resend requests were not made for some missing packets. In addition, requests for resends of continuous sequences of packets are rolled into one.
Expose the advanced settings controlling the resend request logic. The new settings are in the general section:
- resend_control_first_check_time is the time allowed to elapse before a packet is considered missing, defaulting to 0.1 sec. UDP packets don't always arrive in order and they don't need to be re-requested just because they arrive out of sequence. Essentially, therefore, this parameter is to prevent needless resend requests for packets that are already in transit.
- resend_control_check_interval_time is the interval between repeated requests for a missing packet, defaulting to 0.25 seconds.
- resend_control_last_check_time is the time by which the last check should be done before the estimated time of a missing packet's transfer to the output buffer, defaulting to 0.1 seconds. In other words, if a packet is still missing 0.1 seconds before it is due to be transferred to the DAC's output buffer, don't bother asking for a resend.
Exposes two advanced metadata settings related to handling cover art:
- The setting cover_art_cache_directory allows you to specify where cover art files will be cached if Shairport Sync has been built with native D-Bus, MPRIS or MQTT support. The default is /tmp/shairport-sync/.cache/coverart. If you set it to an empty list: "", caching is disabled. This might be useful in, say, an embedded device, or wherever you want to minimise file writing.
- The setting retain_cover_art is part of the diagnostics group. Set it to "yes" to retain cover art cached by the D-Bus, MPRIS or mqtt interfaces. Your directory may fill up if you leave it set!

Version 3.3.2

Bug Fixes

Fix a bug that sometimes caused a crash when a service name was specified in the configuration file. The fix was to be more systematic in allocating and deallocating memory for temporary strings. Thanks to Chris Boot, Ari Sovijarvi, Bernhard Übelacker and Jeroen Massar for the bug report. Fixes Debian Bug report #925577 and supercedes Pull Request #879.
Correct some documentation typos – thanks again to Chris Boot.

Enhancements

Add some settings for controlling the disable_standby_mode.

The first setting is the disable_standby_mode_silence_threshold, which is the amount of audio in the output device's hardware buffer. It should normally be close to the value given in the audio_backend_buffer_desired_length_in_seconds setting. If it drops to this value, silence is added to the buffer to prevent the output device from becoming idle.
The second new setting is the disable_standby_mode_silence_scan_interval which is the time between checks of the output device's hardware buffer.

Version 3.3.1

Bug Fixes

Fix a bug in the MQTT documentation and add sanity checking for the port chosen -- thanks to David Crook.
Fix a bug that caused manual format and rate setting to be ignored -- thanks to Jörg Krause.
Add missing support for format settings S24_LE, S24_BE, S32_LE and S32_BE.
Fix a bug that caused dither to be too loud.
Fix error message for invalid disable_standby_mode choice -- thanks to Tim Curtis at Moode Audio.

Version 3.3

Version 3.3 is focused on stability improvements and also offers a number of enhancements. Here is a selection of the most important:

Enhancements

Automatic alsa output device speed and format selection. The greatest bit depth and the lowest multiple of 44,100 frames per second settings are chosen automatically by default. Manual selection is still available.
Automatic interpolation selection. If the CPU is fast enough, the better-quality soxr interpolation method is chosen. Otherwise basic interpolation is used. Manual selection is still available.
A new active state. New hooks are provided to execute programs before entering and after leaving the active state which covers sequences of play sessions separated by short intervals. This simplifies amplifier switch-on and switch-off, for example.
DAC crackle minimisation. This new feature is intended to minimise pops and crackles caused in some Digital to Analog Converters (DACs) when they transition between active and idle or standby operation. The new alsa-only disable_standby_mode prevents the DAC entering the standby mode by keeping it active, either permanently or while Shairport Sync is in the active state. This feature is switched off by default.
A new backend to interface Shairport Sync to Jack Audio, thanks to the work of Jörn Nettingsmeier.
A new MQTT client interface, thanks to the work of Till Zimmermann.
Changes in logging -- now you should add -u to direct log entries to STDERR (typically the console) rather than the system log. For example, to get logs of verbosity 1 to appear on the console: $ shairport-sync -v -u.
The help menu now lists all alsa output devices found.
Better support for big-endian CPUs.
Shairport Sync accepts AirPlay streams containing CD-quality uncompressed PCM.

Bug Fixes

Lots of bugs – too many to list here – have been fixed that significantly improve the stability of Shairport Sync. The full list is in the Release Notes.

For more details of enhancements and bug fixes, please see the Release Notes for 3.3. Special thanks to gibman.

Version 3.2.2

Please see the Release Notes for 3.2.

Enhancement

Latency calculations have been updated to accommodate changes in iOS 12 and AirPlay connections from macOS Mojave. Thanks to artenverho who first reported the issue.
Formatting of the settings file shairport-sync.conf has been fixed, thanks to the work of roblan.

Bug Fix

Fixed a problem that prevented the run_this_when_volume_is_set script or program from running when the volume control is changed. Thanks to shaven for the report.

Version 3.2.1

Bug Fix

Fix a bug that was causing problems when soxr interpolation was chosen. Problems included instability during or after a play session and possibly an extremely slight click on very loud audio. Thanks are due to hanaguro, FnasBas, priitohlo, David Krmpotić and artenverho.

Version 3.2

Version 3.2 is equivalent to 3.2RC13.

Version 3.2RC13

Adjustment

Reduce the number of attempts that will be made to have a missing packet resent. It seems that in some situations on poor networks, the number of resend requests was causing problems.

Version 3.2RC12

Enhancement

Add a "ProgressString" property to the native D-Bus interface.

Bug Fix

Some code added in RC11 to monitor mutex lock times was causing some annoying issues -- fixed.

Version 3.2RC11

Bug Fixes

Restore compatibility with Synology AudioStation/5.2. Thanks to Jörg Krause for identifying both the issue itself and the likely location of the fix needed. It's not clear if the problem lies with Shairport Sync or Synology – the fix was to ensure that an RTSP reply was sent in one SEND call, which shouldn't be important.
Fix a bug that was causing Shairport Sync to hang very occasionally when a play session was ending. This seems to occur under rare circumstances, therefore many thanks to David Krmpotić both for finding the problem and for his patience in trying out different theories before the bug was finally identified. More long-term work is probably needed here.

Version 3.2RC10

Compatibility Adjustment

Disable the use of all hardware mute mechanisms by default, for compatibility with other applications using the same output card.
Rename the alsa setting mute_using_playback_switch to use_hardware_mute_if_available and make it control volume-based mute as well as playback-switch-based mute.

Version 3.2RC9

Bug Fix

Restore the correct pathname for the Shairport Sync PID file used in FreeBSD and System V Linux installations.

Version 3.2RC8

Bug Fixes

Fix a bug causing a play session to hang up on Cygwin 64. Fix a bug that might cause excessive resend requests. Fix a number of other (apparently) silent bugs.

Version 3.2RC7

Bug Fixes

A very subtle bug that would occasionally cause a loud 80 millisecond buzz when a new track was selected has been located and fixed. Thanks to mistipen and artenverho for help with this.

Version 3.2RC6

Bug Fixes

Restores audio sync with videos on older versions of iOS (prior to iOS 11.2) and macOS by restoring the old way of determining latency for clients identifying with AirPlay user agent strings having a version of 353 (iOS 11.1.2) or earlier. Thanks to Mmoi-Fr for help with this.

Version 3.2RC5

Bug Fixes

When errors occur sending resend requests, back off for 0.5 seconds, rather than 10 seconds, and make the code actually work.
Make the configuration options for including the dbus interface and the mpris interface be --with-dbus-interface and --with-mpris-interface as expected, not --with-dbus and --with-mpris as they actually were.

Version 3.2RC4

Bug Fixes

3.2RC4 now sends resend requests (correctly) in the control channel rather than (incorrectly) over the audio channel as before. This makes it compatible with AirAudio and also makes it conform to the Unofficial AirPlay Protocol Specification. This bug went unnoticed for so long because other AirPlay sources accept resend requests in the audio channel. Thanks to funtax and to Janusz Kowalczyk for bringing the issue to the fore.

Version 3.2RC3

Enhancements

Lost UDP packet resending code improved for better performance on busy or congested networks.

Bug Fixes

3.2RC3 removes fixes some important and long-standing bugs that could make Shairport Sync less resilient on noisy or poor quality networks.

Version 3.2RC2

Bug Fixes

3.2RC2 makes Shairport Sync work with AirAudio, removing a crashing bug, and includes some more debugging code.

Version 3.2RC1

Enhancements

Shairport Sync now offers an IPC interface via D-Bus. It provides an incomplete but functional MPRIS interface and also provides a native Shairport Sync interface. Both provide some metadata and some remote control. The native D-Bus interface permits remote control of the current AirPlay or iTunes client. It includes status information about whether the remote control connection is viable or not, i.e. whether it can still be used to control the client. A remote control connection to the audio client becomes valid when the client starts AirPlaying to Shairport Sync. The connections remains valid until the audio source deselects Shairport Sync for AirPlay, or until the client disappears, or until another client starts AirPlaying to Shairport Sync. After 15 minutes of inactivity, the remote control connection will be dropped.
OpenBSD compatibility. Shairport Sync now compiles on OpenBSD -- please consult the OpenBSD note for details.
A new general option volume_control_profile, for advanced use only, with two options: "standard" which uses the standard volume control profile -- this has a higher transfer profile at low volumes and a lower transfer profile at high volumes -- or "flat" which uses a uniform transfer profile to linearly scale the output mixer's dB according to the AirPlay volume.
Some DACs have a feature that the lowest permissible "attenuation" value that the built-in hardware mixer can be set to is not an attenuation value at all – it is in fact a command to mute the output completely. Shairport Sync has always checked for this feature, basically in order to ignore it when getting the true range of attenuation values offered by the mixer. However, with this enhancement, Shairport Sync can actually use this feature to mute the output where appropriate.
Added compatibility with Swinsian, a Mac music player.

Bug Fixes

Better AirPlay synchronisation. Older versions of Shairport Sync added an 11,025 frame (0.25 seconds) offset to all the latencies negotiated with the sender. This seems now incorrect for AirPlay sources. Accordingly, the logic Shairport Sync uses to determine the extra delay has been revised. The result is better sync with videos, e.g, YouTube, while iTunes and ForkedDaapd synchronisation is unaffected.
Much faster termination of a play session, leading to increased stability playing YouTube audio, etc.
Improved resynchronisation logic should improve performance with slow-to-download YouTube videos.
Dithering is now off when ignore_volume_control is true. Thanks to yejun for working on this.
Better compatibility with TuneBlade -- Shairport Sync honours the latency settings properly now.
Fix timing error when using Airfoil as a source.
Better handling of missing timing packets.
Shairport Sync will now log an unexpectedy dropped or faulty RTSP connection. This might be useful on noisy networks.
Better volume level continuity. In recent versions of iOS (11.2) and mac OS (10.13.2), when play is resumed after a pause, the volume level is not always restored, and, if software volume control is being used, Shairport Sync plays at full volume. This issue has been addressed by storing the last airplay volume setting when a play session ends and using it as a default when a new play session begins.
Better mixer compatibility. A bug in the hardware volume control affected output devices that have hardware mixers but that do not allow the volume to be set in dB. One example is the Softvol plugin in ALSA. Shairport Sync failed silently when presented with such a device when hardware volume control is enabled: the volume events have no effect. The bug has been fixed by adding two missing lines of code to the init() function in audio_alsa.c. Thanks to Jakub Nabaglo for finding and fixing the bug.
A number of bug fixes due to belboj. Many thanks for these!
Enhancements to the handling of quit requests by threads, thanks(again) to belboj!

Other Changes

clip and svip metadata messages are now only generated for a play connection, not for all connections (e.g. connections that just enquire if the service is present).
pfls and prsm metadata messages are less frequent, especially when a play session starts.
Shairport Sync now uses about an extra half megabyte of RAM for compatibility with TuneBlade's option to have a very long latency -- up to five seconds.
Only ask for missing packets to be resent once, and if any error occurs making the request, stop for 10 seconds.
Include the -pthread flag -- including the pthread library with -lpthread isn't always enough.
Add optional timing annotations to debug messages -- see the new settings in the diagnostic stanza of the configuration file.

Updated Documentation

CAR INSTALL and OPENBSD notes added.
Improvements in the documentation relating to scripts -- thanks to Niklas Janz.
Typo fix! Thanks to corbinsantin.

Version 3.1.7

Stable 3.1.5 and 3.1.6 skipped to synchronise the shairport-sync.spec file contents with the release.

Enhancement

The metadata output stream can include a dapo message carrying the DACP port number to be used when communicating with the DACP remote control. This might be useful because the port number is actually pretty hard to find and requires the use of asynchronous mdns operations. You must be using the Avahi mdns back end.

Version 3.1.4

Security Update

The version of tinysvcmdns bundled in Shairport Sync has a buffer overflow bug: "An exploitable heap overflow vulnerability exists in the tinysvcmdns library version 2016-07-18. A specially crafted packet can make the library overwrite an arbitrary amount of data on the heap with attacker controlled values. An attacker needs send a dns packet to trigger this vulnerability." The vulnerability is addressed by additional checking on packet sizes. See also CVE-2017-12087 and Vulnerability in tinysvcmdns. Thanks and Chris Boot for fixing this bug.

Enhancement

The metadata output stream can include a dapo message carrying the DACP port number to be used when communicating with the DACP remote control. This might be useful because the port number is actually pretty hard to find and requires the use of asynchronous mdns operations. You must be using the Avahi mdns back end.

Bug Fix

Somewhere in version 3.x, the softvol plugin got broken as the volume change is not applied anymore. Turned out that, for the softvol plugin, no volume() and parameters() are defined. Thanks to Jörg Krause for locating and fixing this bug.

Version 3.1.3

Bug Fixes

Fixed a bug that prevented Shairport Sync from starting automatically on systems using the System V startup system (e.g. Ubuntu 14.04). The problem was that the directory to be used – /var/run/shairport-sync/ – was deleted on power down and needed to be recreated on startup. In it's absence, Shairport Sync would not start and would report a mysterious daemon error #2.

Version 3.1.2

Shairport Sync is more stable playing audio from YouTube and SoundCloud on the Mac.

Pesky Changes You Should Not Ignore

When you update from a previous version of Shairport Sync, your output device may have been left in a muted state. You should use a command line tool like alsamixer or amixer to unmute the output device before further use.

Change of Default

The default value for the alsa setting mute_using_playback_switch has been changed to "no" for compatibility with other audio players on the same machine. The reason is that when this setting is set to "yes", the output device will be muted when Shairport Sync releases it. Unfortunately, other audio players using the output device expect it to be unmuted, causing problems. Thanks to Tim Curtis at Moode Audio and Peter Pablo for clarifying the issue.

Bug Fixes

Fixed bugs that made Shairport Sync drop out or become unavailable when playing YouTube videos, SoundCloud streams etc. from the Mac. Background: there has been a persistent problem with Shairport Sync becoming unavailable after playing, say, a YouTube clip in a browser on the Mac. Shairport Sync 3.1.2 incorporates a change to how certain AirPlay messages are handled. Introduced in nascent form in 3.1.1, further follow-on changes have improved the handling of player lock and have simplified and improved the handling of unexpected loss of connection. Shairport Sync also now works properly with SoundCloud clips played in a browser on the Mac.
Using infer, a number of silent issues have been detected, such as not checking some calls to malloc to ensure the response is not NULL. Most of these have been addressed by additional checks.

Version 3.1.1

Bug Fixes

A bug in the sndio backend has been fixed that caused problems on some versions of Linux.
A change has been made to how Shairport Sync responds to a TEARDOWN request, which should make it respond better to sequences of rapid termination and restarting of play sessions. This can happen, for example, playing YouTube videos in Safari or Chrome on a Mac.
Choosing soxr interpolation in the configuration file will now cause Shairport Sync to terminate with a message if Shairport Sync has not been compiled with SoX support.
Other small changes.

Version 3.1

Version 3.1 brings two new backends, optional loudness and convolution filters, improvements in non-synchronised backends, enhancements, stability improvements and bug fixes.

New Features

A sndio backend gives Shairport Sync native fully synchronised output on OpenBSD and FreeBSD, thanks to the work of Tobias Kortkamp (t6).
A pa backend now allows Shairport Sync to provide synchronised output on PulseAudio-equipped systems -- many desktop Linuxes use PulseAudio as their sound manager.
Optional loudness and convolution filters can be incorporated in the audio processing chain, thanks to the fantastic work of yannpom.
A volume-change program hook run_this_when_volume_is_set has been added to the general settings stanza to execute an application whenever the volume is changed.

Pesky Changes You Should Know About

The audio_backend_buffer_desired_length_in_seconds and audio_backend_latency_offset_in_seconds settings have been moved from individual backend stanzas to the general stanza. They now have an effect on every type of backend.
If you are using a System V (aka systemv) installation, please note that the default location for PID file has moved -- it is now stored at /var/run/shairport-sync/shairport-sync.pid. This change is needed to improve security a little and to improve compatibility across platforms. If you're not doing anything strange, this should make no difference.

Enhancements

Resynchronisation, which happens when the synchronisation is incorrect by more than 50 ms by default, should be a lot less intrusive when it occurs – it should now either insert silence or skip frames, as appropriate.
The Linux installer has been improved and simplified and a FreeBSD installer introduced.
A new setting, audio_backend_silent_lead_in_time, allows you to set the duration of the period of silence played (the "silent lead-in") before a play session starts.
A new command-line option, --logOutputLevel, allows you to output the volume levels to the log whenever they are changed. This may be useful during setup.
Improvements have been made to the handling of large items of metadata over UDP.
A new command line option, -j, demonizes Shairport Sync without creating a PID file.
A new alsa-only setting, mute_using_playback_switch, is available for advanced use.
Other minor enhancements.

Bug Fixes

Stability improvements. More care has been taken (!) to make code thread-safe, resulting in improved stability.
Conversion from stereo to mono has been fixed to avoid clipping while preserving full resolution. Thanks to Robert Jones (RobDeBagel) for bringing this to notice.
Short intrusions of audio at the start of a new session from the end of the previous session have been eliminated.
Many (many!) miscellaneous bugs fixed.

Version 3.0.2

Bug Fixes

Fixed bugs in the ao, pulseaudio and sndio back ends. Basically they were expecting default sample rate and depth information, and were terminating when they saw explicit rate and depth data.

Version 3.0.1

This update fixes one alarming and potentially very noisy bug and restores the identification of Shairport Sync as "ShairportSync" so that TuneBlade recognises it as an open source application. Bug Fixes

Fixed a bug that was causing Shairport Sync to possibly make a very loud and alarming noise whenever an audio frame was missing.
In 2.8.6, a change was made to the way Shairport Sync identified itself, so that it could be recognised by TuneBlade as an open source application and treated preferentially. That change was inadventently lost in the transition from 2.8.6 to 3.0. Now it's restored.

Version 3.0

Big Update

Version 3 brings in support for 24-bit and 32-bit (and 8 bit!) DACs and for DACs running at multiples of 44,100 samples per second.

The most obvious audible change is if you are using software volume control and can take advantage of 32- or 24-bit DACs. Dithering can now occur on a 32-bit or 24-bit sample rather than on a 16-bit sample, making the noise floor very much lower. This is the case, for example, with a Pimoroni PHAT DAC.

Here is the list of new features:

New Features

8-bit, 16-bit, 24-bit, 24-bit three-byte (S24_3LE and S24_3BE) and 32-bit output to ALSA devices.
44,100, 88,200, 176,400 and 352,800 sample per second output. This is done using simple upsampling. It's only worth doing if 44,100 samples per second output is not available.
Internal processing including software volume control and interpolation is done after sample size and rate conversion.
Apple ALAC decoder support. This needs the libalac library, available at ALAC, to be installed. Add the flag --with-apple-alac to the ./configure arguments. Then you can choose the Apple ALAC decoder in the configuration file.
Support for mbed TLS has been added and the use of PolarSSL is deprecated, as mbed TLS is a development of PolarSSL and PolarSSL itself is not being developed further.
Choose Network Interface. Add a new setting, for advanced users only, in the general section. Use the interface setting to allow you to specify the interface on which to provide the AirPlay service. Omit the setting to get the default, which is to choose the interfaces automatically.
Set Max Volume. Add a new setting, for advanced users only, in the general section. Use the volume_max_db setting to allow you to specify the maximum level to set on the hardware mixer (if chosen) or the built-in software mixer otherwise. The software mixer's range is 0.0 dB to -96.1 dB. The setting must be a number with a decimal point, e.g. 21.3.
An experimental new back end for libsoundio, a C library for cross-platform real-time audio input and output. Many thanks to Serg Podtynnyi. Please see mikebrady#433 for more details.