PipeWire: audio_output "pipewire" with audio_output "fifo" stops audio playback after pause and resume, and sometimes after seek

[VC73]

Bug report

Pipewire output combined with FIFO output stops the audio stream after resume or seek. mpd.conf

audio_output {  
    type               "fifo"  

    name               "toggle_visualizer"

    path               "/tmp/mpd.fifo"

    format             "44100:16:1"
}

audio_output {
    type  "pipewire"
    name  "Pipewire output"
}

Describe the bug

MPD with Pipewire and FIFO output plugins enabled stops streaming audio after pause and resume every time.

It pauses normally, then on resume you can hear a little part of the audio for some milliseconds before the audio playback stops, it also can happen sometimes after a seek, although in this case you cannot hear anything, it just stops playing audio and it's random.

To resume audio playback a restart is necessary, although sometimes audio continues to work after a another pause and resume, for this to happen some time has to have passed after the audio stops, this time can be just seconds or some undefined amount of time.

Expected Behavior

MPD continues to play audio without interruption after resume or seek.

Actual Behavior

MPD stops playing audio after pause and resume, and sometimes after seek.

Version

Music Player Daemon 0.23~git (v0.22.10-446-gbd893e633+)
Copyright 2003-2007 Warren Dukes <warren.dukes@gmail.com>
Copyright 2008-2021 Max Kellermann <max.kellermann@gmail.com>
This is free software; see the source for copying conditions.  There is NO
warranty; not even MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Database plugins:
 simple proxy upnp

Storage plugins:
 local udisks nfs curl

Neighbor plugins:
 upnp udisks

Decoders plugins:
 [mad] mp3 mp2
 [mpg123] mp3
 [vorbis] ogg oga
 [oggflac] ogg oga
 [flac] flac
 [opus] opus ogg oga
 [sndfile] wav aiff aif au snd paf iff svx sf voc w64 pvf xi htk caf sd2
 [audiofile] wav au aiff aif
 [dsdiff] dff
 [dsf] dsf
 [hybrid_dsd] m4a
 [faad] aac
 [mpcdec] mpc
 [wavpack] wv
 [modplug] 669 amf ams dbm dfm dsm far it med mdl mod mtm mt2 okt s3m stm ult umx xm
 [mikmod] amf dsm far gdm imf it med mod mtm s3m stm stx ult uni xm
 [sidplay] sid mus str prg P00
 [wildmidi] mid
 [fluidsynth] mid
 [ffmpeg] 16sv 3g2 3gp 4xm 8svx aa3 aac ac3 adx afc aif aifc aiff al alaw amr anim apc ape asf atrac au aud avi avm2 avs bap bfi c93 cak cin cmv cpk daud dct divx dts dv dvd dxa eac3 film flac flc fli fll flx flv g726 gsm gxf iss m1v m2v m2t m2ts m4a m4b m4v mad mj2 mjpeg mjpg mka mkv mlp mm mmf mov mp+ mp1 mp2 mp3 mp4 mpc mpeg mpg mpga mpp mpu mve mvi mxf nc nsv nut nuv oga ogm ogv ogx oma ogg omg opus psp pva qcp qt r3d ra ram rl2 rm rmvb roq rpl rvc shn smk snd sol son spx str swf tak tgi tgq tgv thp ts tsp tta xa xvid uv uv2 vb vid vob voc vp6 vmd wav webm wma wmv wsaud wsvga wv wve rtp:// rtsp:// rtsps://
 [gme] ay gbs gym hes kss nsf nsfe rsn sap spc vgm vgz
 [pcm]

Filters:
 libsamplerate soxr

Tag plugins:
 id3tag

Output plugins:
 shout null fifo pipe alsa ao oss openal solaris pipewire pulse jack httpd snapcast recorder

Encoder plugins:
 null vorbis opus lame twolame wave flac

Archive plugins:
 [bz2] bz2
 [zzip] zip
 [iso] iso

Input plugins:
 file io_uring archive alsa qobuz curl ffmpeg nfs mms cdio_paranoia

Playlist plugins:
 extm3u m3u pls xspf asx rss soundcloud flac cue embcue

Protocols:
 file:// alsa:// cdda:// ftp:// ftps:// gopher:// hls+http:// hls+https:// http:// https:// mms:// mmsh:// mmst:// mmsu:// nfs:// qobuz:// rtmp:// rtmpe:// rtmps:// rtmpt:// rtmpte:// rtmpts:// rtp:// rtsp:// rtsps:// scp:// sftp:// smb:// srtp://

Other features:
 avahi dbus udisks epoll icu inotify ipv6 systemd tcp un

Log

log doesn't seem to highlight any issues

Aug 06 22:52 : client: [1] process command "status"
Aug 06 22:52 : client: [1] command returned 0
Aug 06 22:52 : client: [1] process command "idle"
Aug 06 22:52 : client: [1] command returned 1
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [1] process command "currentsong"
Aug 06 22:52 : client: [1] command returned 0
Aug 06 22:52 : client: [1] process command "status"
Aug 06 22:52 : client: [1] command returned 0
Aug 06 22:52 : client: [1] process command "idle"
Aug 06 22:52 : client: [1] command returned 1
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "status"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [0] process command "currentsong"
Aug 06 22:52 : client: [0] command returned 0
Aug 06 22:52 : client: [2] process command "status"
Aug 06 22:52 : client: [2] command returned 0
Aug 06 22:52 : client: [2] process command "idle"
Aug 06 22:52 : client: [2] command returned 1

[MaxKellermann]

Confirmed, reproducible. Happens because PipeWire doesn't reactivate a stream after pw_stream_flush() has been called. Can't find any API documentation about it, so I need to try'n'error until it works ...