[Problem]: Can't connect even though device is appearing on network

[djchadderton]

What happened?

I've installed Raspberry Pi OS Trixie light fresh on a Pi Zero with a RP DAC Pro attached and—I think—followed the instructions exactly for installing NQPTP and Shairport.

When I tested it just with the command shairport-sync, the device appeared on the network and I managed to play through it from my iPhone.

I installed it as a service and rebooted the Pi, and also installed Shairport Metadata Reader. After that, it stopped working—it still appears on the network and I can connect, but when I press 'play', after a pause of a few seconds it drops the connection and doesn't play anything.

Running systemctl status shairport-sync doesn't show any issues.

shairport-sync.service - Shairport Sync - AirPlay Audio Receiver
     Loaded: loaded (/usr/lib/systemd/system/shairport-sync.service; enabled; preset: enabled)
    Drop-In: /etc/systemd/system/shairport-sync.service.d
             └─override.conf
     Active: active (running) since Sun 2026-03-15 12:25:49 GMT; 4s ago
 Invocation: e6efbcc846ed4a27a4ee9ab654a4b3ee
   Main PID: 1543 (shairport-sync)
      Tasks: 5 (limit: 176)
        CPU: 1.752s
     CGroup: /system.slice/shairport-sync.service
             └─1543 /usr/local/bin/shairport-sync --log-to-syslog

Mar 15 12:25:49 pi-dac systemd[1]: shairport-sync.service: Scheduled restart job, restart counter is at 1.
Mar 15 12:25:49 pi-dac systemd[1]: Started shairport-sync.service - Shairport Sync - AirPlay Audio Receiver.

However, shairport-sync -v --statistics includes the following:

         0.001201458 "rtsp.c:5316" unable to listen on IPv4 port 7000. The error is: "Address already in use".
         0.000105208 "rtsp.c:5316" unable to listen on IPv6 port 7000. The error is: "Address already in use".
         0.000020417 "rtsp.c:5579" *fatal error: could not establish a service on port 7000 -- program terminating. Is another instance of Shairport Sync running on this device?

No other instance is running. sudo ss -ltnp shows:

State     Recv-Q    Send-Q       Local Address:Port       Peer Address:Port   Process                                      
LISTEN    0         255                0.0.0.0:7000            0.0.0.0:*       users:(("shairport-sync",pid=1543,fd=3))    
LISTEN    0         128                0.0.0.0:22              0.0.0.0:*       users:(("sshd",pid=902,fd=6))               
LISTEN    0         255                   [::]:7000               [::]:*       users:(("shairport-sync",pid=1543,fd=4))    
LISTEN    0         128                   [::]:22                 [::]:*       users:(("sshd",pid=902,fd=7)) 

If I stop the shairport-sync service and use the shairport-sync command again now, when I try playing anything, I get the message:

fatal error: Unexpected SPS_FORMAT_* with index 52 while outputting silence

However, the --statistics log doesn't show the port error.

Relevant log output

0.000663438 "shairport.c:674" looking for configuration file at full path "/etc/shairport-sync.conf"
         0.014124163 "shairport.c:2623" Startup in AirPlay 2 mode, with features 0x405c4a00,0x1c340 on device "2c:cf:67:f5:29:13".
         0.000176562 "shairport.c:2662" Version String: "5.0.1-1-gdc4c334a-AirPlay2-smi10-OpenSSL-Avahi-ALSA-soxr-sysconfdir:/etc"
         0.000022813 "shairport.c:2681" Command Line: "shairport-sync -v --statistics".
         0.000396614 "shairport.c:2725" audio backend is "alsa".
         0.000534896 "shairport.c:3013" disable_resend_requests is off.
         0.000035781 "shairport.c:3015" diagnostic_drop_packet_fraction is 0.000000. A value of 0.0 means no packets will be dropped deliberately.
         0.000021979 "shairport.c:3019" statistics_requester status is 1.
         0.000012709 "shairport.c:3024" rtsp listening port is 7000.
         0.000012135 "shairport.c:3025" udp base port is 6001.
         0.000012292 "shairport.c:3026" udp port range is 10.
         0.000012187 "shairport.c:3027" player name is "Pi-dac".
         0.000011979 "shairport.c:3028" run_this_before_play_begins action is "(null)".
         0.000012396 "shairport.c:3030" run_this_after_play_ends action is "(null)".
         0.000012031 "shairport.c:3031" wait-cmd status is 0.
         0.000011875 "shairport.c:3032" run_this_before_play_begins may return output is 0.
         0.000012292 "shairport.c:3034" run_this_if_an_unfixable_error_is_detected action is "(null)".
         0.000012813 "shairport.c:3036" run_this_before_entering_active_state action is  "(null)".
         0.000012500 "shairport.c:3038" run_this_after_exiting_active_state action is  "(null)".
         0.000012135 "shairport.c:3040" active_state_timeout is  10.000000 seconds.
         0.000016719 "shairport.c:3041" mdns backend "(null)".
         0.000012135 "shairport.c:3043" interpolation setting is "auto".
         0.000012240 "shairport.c:3048" interpolation soxr_delay_threshold is 30000000.
         0.000012604 "shairport.c:3050" resync time is 0.050000 seconds.
         0.000042448 "shairport.c:3051" allow a classic AirPlay session to be interrupted: "no".
         0.000015156 "shairport.c:3053" busy timeout time is 60.
         0.000018333 "shairport.c:3054" drift tolerance is 0.002000 seconds.
         0.000052396 "shairport.c:3055" password is "(null)".
         0.000045833 "shairport.c:3056" default airplay volume is: -24.000000.
         0.000062553 "shairport.c:3057" ignore_volume_control is 0.
         0.000046562 "shairport.c:3061" volume_max_db is not set
         0.000044740 "shairport.c:3062" volume range in dB (zero means use the range specified by the mixer): 0.
         0.000045729 "shairport.c:3065" volume_range_combined_hardware_priority (1 means hardware mixer attenuation is used first) is 0.
         0.000069062 "shairport.c:3069" playback_mode is 0 (0-stereo, 1-mono, 1-reverse_stereo, 2-both_left, 3-both_right).
         0.000046250 "shairport.c:3072" disable_synchronization is 0.
         0.000044792 "shairport.c:3073" use_mmap_if_available is 0.
         0.000073698 "shairport.c:3074" output_format automatic selection is enabled.
         0.000045833 "shairport.c:3079" output_rate automatic selection is enabled.
         0.000099479 "shairport.c:3083" audio backend desired buffer length is 0.200000 seconds.
         0.000115677 "shairport.c:3085" audio_backend_buffer_interpolation_threshold_in_seconds is 0.060000 seconds.
         0.000047917 "shairport.c:3088" audio backend latency offset is 0.000000 seconds.
         0.000046562 "shairport.c:3091" audio backend silence lead-in time is "auto".
         0.000054532 "shairport.c:3095" zeroconf regtype is "_raop._tcp".
         0.000045677 "shairport.c:3096" decoders_supported bit field is 4 (1 == hammerton, 2 == apple, 4 == ffmpeg).
         0.000045885 "shairport.c:3099" decoder_in_use is 4.
         0.000045938 "shairport.c:3100" alsa_use_hardware_mute is 0.
         0.000054531 "shairport.c:3104" no special mdns service interface was requested.
         0.000109739 "shairport.c:3107" configuration file name "/etc/shairport-sync.conf" resolves to "/etc/shairport-sync.conf".
         0.000074532 "shairport.c:3151" loudness_enabled is false.
         0.000058020 "shairport.c:3153" loudness reference level is -16.000000
         0.001554688 "shairport.c:3316" NQPTP is online.
         0.001201458 "rtsp.c:5316" unable to listen on IPv4 port 7000. The error is: "Address already in use".
         0.000105208 "rtsp.c:5316" unable to listen on IPv6 port 7000. The error is: "Address already in use".
         0.000020417 "rtsp.c:5579" *fatal error: could not establish a service on port 7000 -- program terminating. Is another instance of Shairport Sync running on this device?
         1.501666409 "shairport.c:281" "soxr" interpolation has been chosen.
         0.000496041 "shairport.c:1997" normal exit

System Information.

Raspberry Pi Zero 2W
Raspberry Pi DAC Pro

Configuration Information.

>> Display Config Start.

From "uname -a":
 Linux pi-dac 6.12.62+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.62-1+rpt1 (2025-12-18) aarch64 GNU/Linux

From /etc/os-release:
 Debian GNU/Linux 13 (trixie)

From /sys/firmware/devicetree/base/model:
 Raspberry Pi Zero 2 W Rev 1.0

Shairport Sync Version String:
 5.0.1-1-gdc4c334a-AirPlay2-smi10-OpenSSL-Avahi-ALSA-soxr-sysconfdir:/etc

Command Line:
 shairport-sync --displayConfig

Configuration File:
 /etc/shairport-sync.conf

The Configuration file contains no active settings.

>> Display Config End.
>> Goodbye!

PulseAudio or PipeWire installed?

• Check if your system uses a Sound Server.

How did you install Shairport Sync?

Built from source

Check previous issues

• Confirm

[mikebrady]

Thanks for the post. It looks as if Shairport Sync is having trouble accessing the output device:

fatal error: Unexpected SPS_FORMAT_* with index 52 while outputting silence

This is causing it to terminate as soon as it tries to start playing.

Instead of leaving the output_device at "default" win the configuration file, you could try setting it to the actual hardware device directly.

Or (having stopped the service) you could use a command line option to try it out. For example, if the name of the device is hw:0, you could try:

$ shairport-sync -v -- -o hw:0

The -v is to get some diagnostics, and the -o after the -- is to specify the alsa output device name. The -- is important as well.
There is a utility called dacquery you can use to get output device names and capabilities.

[djchadderton]

from the command you suggested, near the top of the output I got:

         0.000025312 "shairport.c:2681" Command Line: "shairport-sync -v -- -o hw:0".
         0.000477752 "shairport.c:2725" audio backend is "alsa".
--: invalid option -- 'o'
         0.000138278 "audio_alsa.c:1464" *warning: Invalid audio option "-?" specified -- ignored.

However, it did list:

    hardware output devices:
      "hdmi:vc4hdmi"
      "hw:Pro"

I specified the output_device as "hw:Pro" in the config file I restarted the service. I connected with my phone and played music and it showed as playing, but it was a long time before any sound actually came out (nearly blew my head off as I had headphones plugged in and assumed it wasn't working). Weirdly, when I pressed pause on my iPhone and it showed it was no longer playing, music was still coming out of the device for a full two minutes more.

But after that, it wouldn't work again. Either I'd select the device on my phone and it would immediately jump back to "iPhone Speaker", or it would try to connect for a while then tell me it couldn't connect, or it would try for a while then tell me there was an "unknown error" with a cryptic Apple error number.

I rebooted and it worked once again then stopped again as above.

[djchadderton]

dacquery gives the following info:

  --- Alsa Version: 1.2.14.
  --- Sound Cards: 2.
  --- Card 0:
        --- Name: "vc4-hdmi".
        --- No mixers found.
        --- Interfaces and Supported Formats:
              >>> Interface "hw:vc4hdmi":
                  This interface appears to be for a disconnected or uninitialized HDMI port. To test it, perform the following steps:
                     (1) connect it to the HDMI device,
                     (2) turn the HDMI device on and select this device as source,
                     (3) reboot and try again.
              >>> Interface "hdmi:vc4hdmi":
                  This interface appears to be for a disconnected or uninitialized HDMI port. To test it, perform the following steps:
                     (1) connect it to the HDMI device,
                     (2) turn the HDMI device on and select this device as source,
                     (3) reboot and try again.
  --- Card 1:
        --- Name: "RPi DAC Pro".
        --- Mixers:
               --------------------------------------------------------------------------------------------------------
              |  Name                              |  Index  |     Min  |     Max  |  Mute dB  |   Min dB  |   Max dB  |
               --------------------------------------------------------------------------------------------------------
              |  Analogue                          |      0  |       0  |       1  |       No  |    -6.00  |     0.00  |
              |  Analogue Playback Boost           |      0  |       0  |       1  |       No  |     0.00  |     0.80  |
              |  Digital                           |      0  |       0  |     207  |      Yes  |  -103.00  |     0.00  |
              |  Max Overclock DAC                 |      0  |       0  |      40  |           |           |           |
              |  Max Overclock DSP                 |      0  |       0  |      40  |           |           |           |
              |  Max Overclock PLL                 |      0  |       0  |      20  |           |           |           |
               --------------------------------------------------------------------------------------------------------
        --- Interfaces and Supported Formats:
              >>> Interface "hw:Pro":
                  This interface supports any rate, format and channel combination from the following table:
                       -------------------------------------------------------------------------------------------------------------
                      |    Rate |              Format |  Channels | Channel Map                                                     |
                       -------------------------------------------------------------------------------------------------------------
                      |    8000 |              S16_LE |         2 |                                                                 |
                      |   11025 |              S24_LE |           |                                                                 |
                      |   16000 |              S32_LE |           |                                                                 |
                      |   22050 |                     |           |                                                                 |
                      |   32000 |                     |           |                                                                 |
                      |   44100 |                     |           |                                                                 |
                      |   48000 |                     |           |                                                                 |
                      |   64000 |                     |           |                                                                 |
                      |   88200 |                     |           |                                                                 |
                      |   96000 |                     |           |                                                                 |
                      |  176400 |                     |           |                                                                 |
                      |  192000 |                     |           |                                                                 |
                      |  352800 |                     |           |                                                                 |
                      |  384000 |                     |           |                                                                 |
                       -------------------------------------------------------------------------------------------------------------

[djchadderton]

Just tried streaming from my ancient MacBook and it seems to work okay at the moment, with latency of about a second rather than a couple of minutes, so maybe it's my phone that's at fault!

[mikebrady]

Apologies — I’m not near my machines right now so didn’t check. It should be -d, but please check in the help message!

The dacquery listing suggests the DAC Pro’s “Digital” is probably the right mixer name for hardware volume control.

My guess is that the “default” output device is the HDMI port, which seems not to be connected, hence the cryptic error 52.

I don’t have a rationale for the delays, I’m afraid. Again, is you stop the service and run it from the command line (with the correct output option!) you might get some more hints.

[mikebrady]

A thing to check is that the WiFi power management is off on the Pi. Please see the TROUBLESHOOTING guide for a bit more.

[djchadderton]

I just tried starting from scratch rather than trying to patch up what I've installed:

• Wiped SD card and reinstalled Trixie 64-bit light.
• Edited config.txt to comment out dtparam=audio=on as per the instructions with the DAC.
• Booted the Pi Zero 2W from the SD card
• Updated everything with apt.
• Installed required packages.
• Followed instructions to install and enable NQPTP.
• Opened alsamixer and "Rpi DAC Pro" came up by default.
• Installed Shairport Sync exactly as per the instructions on Github except with the addition of the --with-metadata option
• Tested it with the shairport-sync command and was able to send music from Apple Music on my ancient MacBook successfully.
• Enabled the Shairport Sync service, disabled WiFi power management and rebooted.
• Music no longer came through on the Pi. When I opened alsamixer, this time, "vc4-hdmi" came up by default and I had to switch to the DAC Pro to see the faders, which were set the same as before.

I don't know where the HDMI audio driver came from or why enabling the Shairport Sync service and rebooting made it the primary device. I can't see any reference to it in config.txt, although there is an entry for dtoverlay=vc4-kms-v3d for, I believe, video.

[mikebrady]

Thank for the post. A couple of things:

1. The issues you are reporting are entirely due to the alsa default device changing on reboot. This is a common problem -- there is plenty of discussion of it on the internet.
2. Fortunately, you can (and should!) avoid referring to the default device -- please see here. By explicitly selecting the output device, as suggested, you become independent of the vagaries of alsa default output device selection.
3. Shairport Sync has no effect on which device is chosen as the alsa default.

We hope this helps!

[djchadderton]

That helped a lot, thanks Mike!

I've been dabbling with Linux for quite a while and audio since the days of cueing up cassettes with a biro, but Linux audio drivers aren't something I've had to deal with before so I haven't seen the Internet chat.

But it now seems to be working, and I've even got the Shairport Sync Metadata Reader working, though I'm not sure what to do with the data from it yet.

I'll plug it into my 40-year-old hifi amp and think about getting a little screen for it. These little Pi Zeros are amazing.

Thanks a lot.