[Problem]: Error identifying output sample formats

[nicolas314]

What happened?

Getting a crash with shairport-sync (shairport-sync-5.0.4-r0) on Alpine v3.24 (kernel 6.18.40-0-lts).
The audio backend is ALSA. Same crash with a USB audio device or the motherboard sound system, and everything works fine with mpg123 via ALSA.
Program starts fine, but when a client connects it hangs with:

        15.333753904 "audio.c:1043" output configuration search for request: S16/44100/2 failed.
         0.000075084 "player.c:2406" *fatal error: An unknown format was encountered while choosing output bit depth. Please check your configuration and settings.

I tried all possible configuration settings and they all lead to the same outcome.
This works fine on Alpine 3.23 (shairport-sync-4.3.7-r1 and kernel 6.12.85) with various sound cards behind ALSA. Playing sounds with e.g. mpg123 works fine through ALSA for all versions.

I tried compiling the shairport-sync developement branch and get the same behaviour. I suspect a change in ALSA between kernel versions, that triggers an uncaught error in shairport-sync, but not sure.

Relevant log output

15.333753904 "audio.c:1043" output configuration search for request: S16/44100/2 failed.
         0.000075084 "player.c:2406" *fatal error: An unknown format was encountered while choosing output bit depth. Please check your configuration and settings.

System Information.

Raspberry Pi 3B running Alpine Linux v3.23 and v3.24. Sound through either USB audio or Raspberry Pi jack, through ALSA.

Configuration Information.

general =
{
    name = "office";
    ignore_volume_control = "yes";
    //service_type = "airplay2";
};

audio_backend = "alsa";

alsa =
{
    output_device = "default";
    mixer_device = "default";
    output_format = "S32";
};

diagnostics =
{
   log_output_to = "syslog";
   log_verbosity = 1 ;
};

PulseAudio or PipeWire installed?

• Check if your system uses a Sound Server.

How did you install Shairport Sync?

A package manager (apt, apt install, yum, pkg, etc.)

Check previous issues

• Confirm

[mikebrady]

Thanks for the report. (BTW, Shairport Sync is not actually "crashing" -- it is doing an orderly shutdown because it can't continue.)

Instead of "S32", try "S32_LE" on the alsa output_format. Better still, remove (or comment out) all settings that are meant to set to the default setting, thus:

general =
{
    name = "office";
    ignore_volume_control = "yes";
    //service_type = "airplay2";
};

// audio_backend = "alsa";

alsa =
{
    // output_device = "default";
    // mixer_device = "default";
    // output_format = "S32";
};

diagnostics =
{
   // log_output_to = "syslog";
   log_verbosity = 1 ;
};

Then see what works. Shairport Sync will default to the alsa backend, and will choose the best rate, format and channel count your DAC has available to suit the input. If you enable statistics in the diagnostics section of the configuration file, then each time Shairport Sync starts to play, it will log information about the input and output formats.

Once things are working, you can experiment with settings, but a suggestion is to make one change at a time, ensuring it is working as expected before moving to the next one.

Another thing you could do to find out more about your DAC is to run dacquery, which will list the capabilities of all your DACs.

(BTW, log_output_to = ... is now obsolete and is ignored.)

[nicolas314]

Agreed, it does not crash, it becomes unresponsive and would not respond to kill -15, has to be shutdown with kill -9. Seems that's a bug you corrected in #2234 (thanks!). With the development branch the program shuts down cleanly but still same error and no sound.

I just tried with:

general =
{
    name = "office";
    ignore_volume_control = "yes";
    //service_type = "airplay2";
};

//audio_backend = "alsa";

alsa =
{
    //output_device = "default";
    //mixer_device  = "default";
    //output_format = "S32";
};

diagnostics =
{
    statistics="yes";
    log_verbosity = 1 ;
};

That configuration works fine on Alpine 3.23.
That same configuration hangs on Alpine 3.24 (kernel 6.18) with shairport-sync from apk (5.0.4-r0) and local version compiled from development branch. Only difference I see in the latter case is the program shuts down instead of hanging. Final words are:

      17.791219890 "audio.c:1043" output configuration search for request: S16/44100/2 failed.
        0.000068137 "player.c:2406" *fatal error: An unknown format was encountered while choosing output bit depth. Please check your configuration and settings.

Let me know if there are any more tests I could do to locate the issue?
Thanks!

[mikebrady]

Thanks! Could you run dacquery and post the results, please?

[nicolas314]

I reverted the Raspberry Pi 3 to Alpine v3.23 to keep enjoying sound. Now moving to an Intel NUC under Alpine v3.24 which exhibits the same behaviour. Here is the output of dacquery for the USB DAC:

  --- Card 1:
        --- Name: "UACDemoV1.0".
        --- Mixer:
               --------------------------------------------------------------------------------------------------------
              |  Name                              |  Index  |     Min  |     Max  |  Mute dB  |   Min dB  |   Max dB  |
               --------------------------------------------------------------------------------------------------------
              |  PCM                               |      0  |       0  |     147  |       No  |   -28.37  |    -0.94  |
               --------------------------------------------------------------------------------------------------------
        --- Interfaces and Supported Formats:
              >>> Interface "hw:UACDemoV10":
              >>> Interface "iec958:UACDemoV10":
                  These interfaces support any rate, format and channel combination from the following table:
                       -------------------------------------------------------------------------------------------------------------
                      |    Rate |              Format |  Channels | Channel Map                                                     |
                       -------------------------------------------------------------------------------------------------------------
                      |   48000 |              S16_LE |         2 | FL FR                                                           |
                       -------------------------------------------------------------------------------------------------------------

[nicolas314]

Forcing the choice does not help. Just tried:

audio_backend = "alsa";
alsa =
{
    output_device = "default";
    mixer_device  = "default";
    output_format = "S16_LE";
    output_rate = 48000;
};

[mikebrady]

Great, thanks. It looks as if the output device only does 48,000 frames per second.

So, two things:

1. I have noticed that this has happened before with a (very good quality!) Apple USB-C to headphone jack. In older versions of Linux, it could run at both 44,100 and 48,000 fps, but in newer versions of Linux at that time, only 48,000. Thus, maybe this is a side-effect of a new Linux?

2. You haven't specified Shairport Sync's version string ($ shairport-sync --V). If it was built without AirPlay 2 or FFmpeg support, then it is only capable of 44,100 fps output and can't transcode. However, if you build it with FFmpeg support, it will transcode automatically.

[nicolas314]

Got it, makes sense. The logs I provided are for a crappy 20€ USB speaker connected to an x86 NUC, and the version I compiled does not have support for ffmpeg or Airplay2, so that explains it. The alpine-packaged version does not have those either (4.3.7-OpenSSL-Avahi-ALSA-pa-pw-stdout-pipe-soxr-metadata-dbus-mpris-sysconfdir:/etc). Let me recompile with ffmpeg support and report what I get.

On the RPi3 the DAC I use is a higher-quality SMSL with more capabilities

Playback:
  Status: Stop
  Interface 1
    Altset 1
    Format: S16_LE
    Channels: 2
    Endpoint: 0x04 (4 OUT) (ADAPTIVE)
    Rates: 44100, 48000, 96000, 192000, 384000
    Data packet interval: 125 us
    Bits: 16
    Channel map: FL FR
  Interface 1
    Altset 2
    Format: S24_3LE
    Channels: 2
    Endpoint: 0x04 (4 OUT) (ADAPTIVE)
    Rates: 44100, 48000, 96000, 192000, 384000
    Data packet interval: 125 us
    Bits: 24
    Channel map: FL FR
  Interface 1
    Altset 3
    Format: S32_LE
    Channels: 2
    Endpoint: 0x04 (4 OUT) (ADAPTIVE)
    Rates: 44100, 48000, 96000, 192000, 384000
    Data packet interval: 125 us
    Bits: 32
    Channel map: FL FR

Let me go back to the RPi3, switch it to Alpine 3.24 (just another SD card), see what I get and come back to you later.

[nicolas314]

Including FFmpeg seems to have solved most of my issues. A million thanks!
In details:

I am using the main git branch for shairport-sync, compiling against FFmpeg (on alpine: ffmpeg-dev). Now it works everywhere: NUC, RPI3, any USB audio device I can put my hands on. Next step is probably to get in touch with the Alpine maintainers to suggest adding FFmpeg to their packaged version of shairport-sync. Good!

There is still a missing bit though. With a USB DAC that reports

# cat /proc/asound/card0/stream0
SMSL AUDIO SMSL AD18 AMP at usb-3f980000.usb-1.5, full speed : USB Audio

Playback:
  Status: Stop
  Interface 1
    Altset 1
    Format: S24_3LE
    Channels: 2
    Endpoint: 0x01 (1 OUT) (ADAPTIVE)
    Rates: 44100, 48000, 88200, 96000
    Bits: 24
    Channel map: FL FR

And that setup:

alsa =
{
    output_device = "default";
    mixer_device = "default";
    //output_format = "S24_3LE";
    output_rate = 44100;
};

i.e. I am trying to force the output rate to 44100, shairport-sync goes back to the error described above:

         0.159884180 "audio.c:1043" output configuration search for request: S16/44100/2 failed.
         0.000232238 "player.c:1034" Error setting the configuration of the output backend.
         0.000095677 "player.c:2432" *fatal error: An unknown format was encountered while choosing output bit depth. Please check your configuration and settings.

I understand S16/44100/2 failed because the device only supports 24 bits, but why doesn't it try S24_3LE/44100/2 before it stops?
Was there a recent change in the kernel that ends up with a different ALSA behaviour maybe?

[mikebrady]

Thanks for the update -- it's good to hear that you're making headway.

I don't know why it's not picking S24_3LE -- it may well be a bug in Shairport Sync. If you could run Shairport Sync with the maximum level of verbosity -- 3 -- and post the results, it may help narrow down the problem.

[nicolas314]

That's the log output for search_for_suitable_configuration() when trying to force output_rate=44100

         0.000039688 "player.c:2371" set up the output chain to ALAC/44100/S16_LE/2 for FFmpeg.
         0.013403047 "audio.c:960" check for an exact multiple of 44100 with 2 channels.
         0.000120885 "audio.c:988" check for the next highest rate above 44100 with 2 channels.
         0.000046458 "audio.c:1006" check for the next lowest rate below 44100 with 2 channels.
         0.000043229 "audio.c:960" check for an exact multiple of 44100 with 3 channels.
         0.000040000 "audio.c:988" check for the next highest rate above 44100 with 3 channels.
         0.000041510 "audio.c:1006" check for the next lowest rate below 44100 with 3 channels.
         0.000040209 "audio.c:960" check for an exact multiple of 44100 with 4 channels.
         0.000039270 "audio.c:988" check for the next highest rate above 44100 with 4 channels.
         0.000039844 "audio.c:1006" check for the next lowest rate below 44100 with 4 channels.
         0.000040260 "audio.c:960" check for an exact multiple of 44100 with 5 channels.
         0.000049115 "audio.c:988" check for the next highest rate above 44100 with 5 channels.
         0.000035937 "audio.c:1006" check for the next lowest rate below 44100 with 5 channels.
         0.000047969 "audio.c:960" check for an exact multiple of 44100 with 6 channels.
         0.000040052 "audio.c:988" check for the next highest rate above 44100 with 6 channels.
         0.000084010 "audio.c:1006" check for the next lowest rate below 44100 with 6 channels.
         0.000041302 "audio.c:960" check for an exact multiple of 44100 with 7 channels.
         0.000039167 "audio.c:988" check for the next highest rate above 44100 with 7 channels.
         0.000052969 "audio.c:1006" check for the next lowest rate below 44100 with 7 channels.
         0.000040677 "audio.c:960" check for an exact multiple of 44100 with 8 channels.
         0.000039062 "audio.c:988" check for the next highest rate above 44100 with 8 channels.
         0.000039792 "audio.c:1006" check for the next lowest rate below 44100 with 8 channels.
         0.000039322 "audio.c:960" check for an exact multiple of 44100 with 1 channels.
         0.000043802 "audio.c:988" check for the next highest rate above 44100 with 1 channels.
         0.000044740 "audio.c:1006" check for the next lowest rate below 44100 with 1 channels.
         0.000041510 "audio.c:1043" output configuration search for request: S16/44100/2 failed.
         0.000076875 "player.c:1034" Error setting the configuration of the output backend.
         0.000040938 "player.c:2432" *fatal error: An unknown format was encountered while choosing output bit depth. Please check your configuration and settings.

And that's the log output for automatic discovery of the best config:

         0.000019583 "player.c:2371" set up the output chain to ALAC/44100/S16_LE/2 for FFmpeg.
         0.012670237 "audio.c:960" check for an exact multiple of 44100 with 2 channels.
         0.000118958 "audio.c:988" check for the next highest rate above 44100 with 2 channels.
         0.000050833 "audio.c:1034" output configuration search for request: S16/44100/2, succeeded with response: 48000/S16_LE/2.
         0.000067084 "player.c:591" Connection 1: outgoing audio switching to: 48000/S16_LE/2.
         0.000047187 "audio_alsa.c:1600" alsa: setting output configuration to 48000/S16_LE/2.

Running through a debugger I found something a bit puzzling, a comparison if (local_rate < rate) where both local_rate and rate are 44100. Not quite sure if I understood the search algorithm though.

As a reminder: the DAC supports both 44100 and 48000

Playback:
  Status: Stop
  Interface 1
    Altset 1
    Format: S24_3LE
    Channels: 2
    Endpoint: 0x01 (1 OUT) (ADAPTIVE)
    Rates: 44100, 48000, 88200, 96000
    Bits: 24
    Channel map: FL FR

[mikebrady]

Thanks -- we'll take a look.

[mikebrady]

I understand S16/44100/2 failed because the device only supports 24 bits, but why doesn't it try S24_3LE/44100/2 before it stops?

Would you be good enough to post two things:

1. run $ shairport-sync --displayConfig and
2. run dacquery on the problematic system,

and post the results, please?