New Feature ? PipeWire audio system replaces the PulseAudio system.

[James7zy]

New Feature ?
I want to use PipeWire instead of PulseAudio system. I think is that PulseAudio and PipeWireare at the same level，so I just change the configuration 'STREAM, unique-id=PipeWire, type=p'. I don't know whether it's correct.
Or should I write new code to adapt PipeWire system . Could you give me some advices.

PipeWire home page: https://pipewire.org/

I have used following configuration, but domainU does not work. I have installed PipeWire in domain0 and shut down all PulseAudio services.

vsnd = [
[ 'CARD, buffer-size=262144, short-name=VCard, long-name=Virtual sound card',
'PCM, name=vsndp',
'STREAM, unique-id=PipeWire, type=p',
'STREAM, unique-id=PipeWire, type=c'
]
]

​ I have checked “unique-id” process in Xen4.15.1. It just give it an id to process in backend.

if (MATCH_OPTION(XENSND_FIELD_STREAM_UNIQUE_ID, param, oparg)) {
            stream->unique_id = strdup(oparg);

#define MATCH_OPTION(prefix, arg, oparg) \
            match_option_size((prefix "="), sizeof((prefix)), (arg), &(oparg))

int match_option_size(const char *prefix, size_t len,
                                char *arg, char **argopt)
          {
              int rc = strncmp(prefix, arg, len);
              if (!rc) *argopt = arg+len;
              return !rc;
          }

​ I have read front code in linux5.11.0. It just use ALSA abstract interface to create CARD、PCM and STREAM,So i think front not to rewirite,Only just to adapt pipewire system in SND_BE?

[al1img]

Yes, no need to change the front end. Backend (snd_be) doesn't support PipeWire as a sound backend. There are two approaches to use PipeWire:

1. Add PipeWire support to snd_be. For this purpose PipeWire pcm device class should be implemented. This class should implement SoundItf::PcmDevice interface. See how it is done for PulseAudio (PulsePcm class).
2. Use PipeWire PulseAudio server to convert PulseAudio protocol to PipeWire protocol. See https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-PulseAudio. No need for snd_be modification in this case.

[James7zy]

@al1img

Thank you very much.
​ Could i ask you another questiones about alsa configuration? when i use following configuration alsa can works,but there are some errors. I am very confused about that. I think when I use this configuration ,backend(SND_BE) sholud give some error informaion. Or it is an invalid configuration.
​ This configuration can play normally, but cannot record. If i use "STREAM, unique-id=alsa < pipewire > ", it has the same scene.

Thank you give me a solution that adapts to pipewire audio system.

vsnd = [
        [ 'CARD, buffer-size=262144, short-name=VCard, long-name=Virtual sound card, sample-rates=44100, sample-formats=s16_le',
            'PCM, name=vsnd', 'STREAM, unique-id=alsa<pulse>, type=p', 'STREAM, unique-id=alsa<pulse>, type=c'
        ]
]

[al1img]

What are the errors exactly? Are you able to record with CLI arecord tool using the specified ALSA device?

[James7zy]

Hi @al1img ,
Thank you for your reply.

​ I will provide more information to discuss this issue.

1. Playback and Capture are normal in domain0.

2. configuraton:unique-id=alsa for Xen.

# Sound cards
vsnd = [ 
		[ 'CARD, buffer-size=1310720, short-name=VCard, long-name=Virtual sound card, channels-max=2,sample-rates=8000;22050;44100;48000, sample-formats=s8;u8;s16_le;s16_be;u16_le;u16_be;s24_le;s24_be;u24_le;u24_be;s32_le;s32_be;u32_le;u32_be;f32_le;f32_be;f64_le;f64_be;iec958_subframe_le;iec958_subframe_be;mu_law;a_law;ima_adpcm;mpeg;gsm',
			'PCM, name=vsnd', 'STREAM, unique-id=alsa<pipewire>, type=p', 'STREAM, unique-id=alsa<pipewire>, type=c'
		]
]

Start domain-u with this configuration. pipewire PCM device created successfully.Both front-end and back-end are connected successfully.

Playback

• Playback has some underrun occurred in backend.Using the player on domain-U can hear the sound but there are some noise.
  

Capture

• The stream of capture has created in frontend.
  

using arecord in domain-U is unnormal.

arecord -t wav test.wav

• The information of SND_BE :

  Frame:0 bytes:0,state:3
  

Recording with tool audacity has the same result.

Question:

Q1.
Is this configuration reasonable?

 unique-id=alsa<pipewire>

Q2:
Is this unexpected error about 'underrun occurred' during playback related to buffer-size parameter in the xl-cfg?

Q3:
Why the recording is not normal？Could you give me some advices?

Kernel version:

Frontend: Linux5.11.0

Backend: snd_be release v0.2.1

Xen :xen-4.15.1

Domain0: AGL linux.

DomainU:Ubuntu 20.04

[James7zy]

Yes, no need to change the front end. Backend (snd_be) doesn't support PipeWire as a sound backend. There are two approaches to use PipeWire:

1. Add PipeWire support to snd_be. For this purpose PipeWire pcm device class should be implemented. This class should implement SoundItf::PcmDevice interface. See how it is done for PulseAudio (PulsePcm class).

**Do you have any development plans for SND_BE with support for pipewire ?

[al1img]

Q1: Yes, once alsa device pipewire exists in Dom0.

Q2: Yes, this error relates to the buffer-size parameter. For Alsa backend, this parameter should be the same as real device buffer. Can be obtained by the following command on Dom0: aplay -D pipewire --dump-hw-params some_wave_file.wav (BUFFER_SIZE).

Q3: Regardless of underrun error, I see there are successful writes to the PCM device as well. Does read error occur immediately after launching arecord command or after some period of time?

To resolve the issue I suggest the following:

• check playback and record for the pipewire device on Dom0: option -D pipewire for aplay and arecord commands;

Playback and Capture are normal in domain0

• adjust the buffer size;
• or you can try to switch to pulse audio backend, this backend is more tolerant to the buffer size.

**Do you have any development plans for SND_BE with support for pipewire ?

Not yet, but we are happy to collaborate on this.