CPAL not finding devices (ALSA, Linux, Raspberry Pi) / CPAL does not support devices that only does recording?

[JonasRSV]

CPAL on raspberry pi does not find or pick any usable devices.

Printing all input devices

    for device in cpal::default_host().input_devices().unwrap() {
        println!("Found {}", device.name().unwrap());
    }

Gives

ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dsnoop.c:575:(snd_pcm_dsnoop_open) The dsnoop plugin supports only capture stream
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave

The output of arecord -L gives

null
    Discard all samples (playback) or generate zero samples (capture)
default:CARD=Camera
    USB2.0 Camera, USB Audio
    Default Audio Device
sysdefault:CARD=Camera
    USB2.0 Camera, USB Audio
    Default Audio Device
front:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    Front speakers
surround21:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    Direct sample mixing device
dsnoop:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    Direct sample snooping device
hw:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    Direct hardware device without any conversions
plughw:CARD=Camera,DEV=0
    USB2.0 Camera, USB Audio
    Hardware device with all software conversions

I have used alsa directly on the same raspberry pi and it works, what could be the reason why cpal does not find devices using alsa? :/

E.g this code

https://gist.github.com/albanpeignier/104902 can record fine with for example

gcc -o alsa-record-example -lasound simple_alsa.c && ./alsa-record-example default:CARD=Camera

audio interface opened
hw_params allocated
hw_params initialized
hw_params access setted
hw_params format setted
hw_params rate setted
hw_params channels setted
hw_params setted
hw_params freed
audio interface prepared
buffer allocated
read 0 done
read 1 done
read 2 done
read 3 done
read 4 done
read 5 done
read 6 done
read 7 done
read 8 done
read 9 done
buffer freed
audio interface closed

If I try to record with CPAL I get

A backend-specific error has occurred: ALSA function 'snd_pcm_open' failed with error 'ENOENT: No such file or directory'

If i print what device CPAL picks it says

Using device default

But that is curious since it found no device? :)

What would be next steps to get this to work with CPAL?

I am using CPAL for https://github.com/JonasRSV/Friday here is the specific code if it is relevant: https://github.com/JonasRSV/Friday/blob/main/friday/audio-io/src/lib.rs#L55 :)

[JonasRSV]

Using the rust crate alsa directly I am able to see my cards and devices on the raspberry pi

        for card in alsa::card::Iter::new() {
            println!("Card {}", card.unwrap().get_name().unwrap());
            let iface = CString::new("pcm");

            for device in alsa::device_name::HintIter::new(Some(&card.unwrap()), &iface.unwrap()).unwrap() {
                println!("Device {}", device.name.unwrap());

            }
        }

Gives

Card bcm2835 Headphones
Device default:CARD=Headphones
Device sysdefault:CARD=Headphones
Device dmix:CARD=Headphones,DEV=0
Device dsnoop:CARD=Headphones,DEV=0
Device hw:CARD=Headphones,DEV=0
Device plughw:CARD=Headphones,DEV=0
Card USB2.0 Camera
Device default:CARD=Camera
Device sysdefault:CARD=Camera
Device front:CARD=Camera,DEV=0
Device surround21:CARD=Camera,DEV=0
Device surround40:CARD=Camera,DEV=0
Device surround41:CARD=Camera,DEV=0
Device surround50:CARD=Camera,DEV=0
Device surround51:CARD=Camera,DEV=0
Device surround71:CARD=Camera,DEV=0
Device iec958:CARD=Camera,DEV=0
Device dmix:CARD=Camera,DEV=0
Device dsnoop:CARD=Camera,DEV=0
Device hw:CARD=Camera,DEV=0
Device plughw:CARD=Camera,DEV=0

[JonasRSV]

Trying to print all devices with cpal

    for device in cpal::default_host().devices().unwrap() {
        println!("Found device {}", device.name().unwrap());
    }

Gives

Found Host ALSA
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dsnoop.c:575:(snd_pcm_dsnoop_open) The dsnoop plugin supports only capture stream
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave
Found device default:CARD=Headphones
Found device sysdefault:CARD=Headphones
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
Found device dmix:CARD=Headphones,DEV=0
ALSA lib pcm_dsnoop.c:575:(snd_pcm_dsnoop_open) The dsnoop plugin supports only capture stream
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave
Found device hw:CARD=Headphones,DEV=0
Found device plughw:CARD=Headphones,DEV=0
Using device default

I think maybe something is going wrong in the iterator

here: https://github.com/RustAudio/cpal/blob/master/src/host/alsa/enumerate.rs#L21

because this loc https://github.com/RustAudio/cpal/blob/master/src/host/alsa/enumerate.rs#L13 contains the correct answer.

        for device in alsa::device_name::HintIter::new_str(None, "pcm").unwrap() {
            println!("Device with new_str {}", device.name.unwrap());
        }

Device with new_str null
Device with new_str default:CARD=Headphones
Device with new_str sysdefault:CARD=Headphones
Device with new_str dmix:CARD=Headphones,DEV=0
Device with new_str dsnoop:CARD=Headphones,DEV=0
Device with new_str hw:CARD=Headphones,DEV=0
Device with new_str plughw:CARD=Headphones,DEV=0
Device with new_str default:CARD=Camera
Device with new_str sysdefault:CARD=Camera
Device with new_str front:CARD=Camera,DEV=0
Device with new_str surround21:CARD=Camera,DEV=0
Device with new_str surround40:CARD=Camera,DEV=0
Device with new_str surround41:CARD=Camera,DEV=0
Device with new_str surround50:CARD=Camera,DEV=0
Device with new_str surround51:CARD=Camera,DEV=0
Device with new_str surround71:CARD=Camera,DEV=0
Device with new_str iec958:CARD=Camera,DEV=0
Device with new_str dmix:CARD=Camera,DEV=0
Device with new_str dsnoop:CARD=Camera,DEV=0
Device with new_str hw:CARD=Camera,DEV=0
Device with new_str plughw:CARD=Camera,DEV=0

[JonasRSV]

Yes I think the problem is this: https://github.com/RustAudio/cpal/blob/master/src/host/alsa/enumerate.rs#L34

Does CPAL only work with devices that have playback and recording?

my device only have recording..

Is this something that you don't want to support, or can supporting devices with only recording be added?

[JonasRSV]

So this works fine

        for device in alsa::device_name::HintIter::new_str(None, "pcm").unwrap() {
            let name = device.name.unwrap();
            let has_available_input = {
                let capture_handle =
                    alsa::pcm::PCM::new(&name, alsa::Direction::Capture, true);
                capture_handle.is_ok()
            };

            if has_available_input {
                println!("Is recording device {}", name);
            }
        }

Is recording device null
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave
Is recording device default:CARD=Camera
Is recording device sysdefault:CARD=Camera
Is recording device front:CARD=Camera,DEV=0
Is recording device surround21:CARD=Camera,DEV=0
Is recording device surround40:CARD=Camera,DEV=0
Is recording device surround41:CARD=Camera,DEV=0
Is recording device surround50:CARD=Camera,DEV=0
Is recording device surround51:CARD=Camera,DEV=0
Is recording device surround71:CARD=Camera,DEV=0
Is recording device iec958:CARD=Camera,DEV=0
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
Is recording device dsnoop:CARD=Camera,DEV=0
Is recording device hw:CARD=Camera,DEV=0
Is recording device plughw:CARD=Camera,DEV=0

[JonasRSV]

But this does not

        for device in alsa::device_name::HintIter::new_str(None, "pcm").unwrap() {
            let name = device.name.unwrap();
            let io = device.direction;

            if let Some(io) = io {
                if io != alsa::Direction::Playback {
                    continue;
                }
            }
            let has_available_input = {
                let capture_handle =
                    alsa::pcm::PCM::new(&name, alsa::Direction::Capture, true);
                capture_handle.is_ok()
            };

            if has_available_input {
                println!("Is recording device {}", name);
            }
        }

Is recording device null
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave

[JonasRSV]

Printing the io

        for device in alsa::device_name::HintIter::new_str(None, "pcm").unwrap() {
            let name = device.name.unwrap();
            let io = device.direction;

            if let Some(io) = io {
                println!("device {} io: {:?}", name, io);
                if io != alsa::Direction::Playback {
                    continue;
                }
            }
            let has_available_input = {
                let capture_handle =
                    alsa::pcm::PCM::new(&name, alsa::Direction::Capture, true);
                capture_handle.is_ok()
            };

            if has_available_input {
                println!("Is recording device {}", name);
            }
        }

Is recording device null
device default:CARD=Headphones io: Playback
device sysdefault:CARD=Headphones io: Playback
device dmix:CARD=Headphones,DEV=0 io: Playback
ALSA lib pcm_dmix.c:1043:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
device dsnoop:CARD=Headphones,DEV=0 io: Playback
ALSA lib pcm_dsnoop.c:638:(snd_pcm_dsnoop_open) unable to open slave
device hw:CARD=Headphones,DEV=0 io: Playback
device plughw:CARD=Headphones,DEV=0 io: Playback
device default:CARD=Camera io: Capture
device sysdefault:CARD=Camera io: Capture
device front:CARD=Camera,DEV=0 io: Capture
device surround21:CARD=Camera,DEV=0 io: Capture
device surround40:CARD=Camera,DEV=0 io: Capture
device surround41:CARD=Camera,DEV=0 io: Capture
device surround50:CARD=Camera,DEV=0 io: Capture
device surround51:CARD=Camera,DEV=0 io: Capture
device surround71:CARD=Camera,DEV=0 io: Capture
device iec958:CARD=Camera,DEV=0 io: Capture
device dmix:CARD=Camera,DEV=0 io: Capture
device dsnoop:CARD=Camera,DEV=0 io: Capture
device hw:CARD=Camera,DEV=0 io: Capture
device plughw:CARD=Camera,DEV=0 io: Capture

So If I understand it correctly, the iterator only lets through devices that have recording and playback capabilities, or only playback. But not only recording?

Can't that if-statement just be dropped or is there some problem with having only recording? :)

[mitchmindtree]

It sounds like this is a bug - it's very possible that most folks using ALSA have gotten lucky so far by using devices that happen to support both capture and playback. Thanks for the detailed issue!

A PR (with all examples tested) would certainly be very welcome.

[JonasRSV]

Yes i'd be happy to look into creating a PR, I currently have exams coming up though so it won't be until the end of December.

I think most people won't be affected by this, because CPAL automatically picks the 'default' device, and often the 'default' device is the one that the users wants used. But on raspberry PI the default device does not work since the PI has no sound card.

I worked around this by changing the default device on the PI to be the device I wanted, so to clarify, CPAL works with 'record only' devices. But it does not detect them, using ALSA at least. So as long as the 'record only' device is the 'default' device it is no problem.

But yes not having to change the default device and have CPAL be able to see 'record only' devices would be nice and i'll look into it later in December :)