Add --dump-hw-params option (alsa backend)

[JasonLG1979]

This function in the alsa backend (along with the other bits necessary) could add the option to dump the hardware parameters of a device mimicking the output of aplay's --dump-hw-params option.

// needs Output from alsa
// use alsa::{Direction, Error, Output, ValueOr};

...

fn dump_hw_params(dev_name: &str) {
    let pcm = PCM::new(dev_name, Direction::Playback, false).unwrap();
    let hwp = HwParams::any(&pcm).unwrap();
    let mut output = Output::buffer_open().unwrap();
    hwp.dump(&mut output).unwrap();

    println!("\nHW Params of device {}\n", dev_name);
    println!("--------------------\n");
    println!("{}", output);
    println!("--------------------\n");
    exit(0);
}

The function would take the same arguments as --device so for example a user could do librespot --dump-hw-params hw:2,0 and they would get something like this:

HW Params of device hw:2,0

--------------------

ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S16_LE S24_3LE
SUBFORMAT:  STD
SAMPLE_BITS: [16 24]
FRAME_BITS: [32 48]
CHANNELS: 2
RATE: [32000 96000]
PERIOD_TIME: [1000 4096000]
PERIOD_SIZE: [32 131072]
PERIOD_BYTES: [128 524288]
PERIODS: [2 1024]
BUFFER_TIME: (666 8192000]
BUFFER_SIZE: [64 262144]
BUFFER_BYTES: [256 1048576]
TICK_TIME: ALL

--------------------

I think it would be super helpful for debugging configuring.

[kingosticks]

My opinion is to add this info to the (debug) logging - if it's not already there- but this is not necessary as an extra dedicated command line argument.

[JasonLG1979]

Or an even better option would be to filter out devices that are not compatible and show what librespot formats the device supports? So it would show something like this:

Compatible alsa devices:

----------------------------------------

Device:

hw:CARD=DAC,DEV=0

Description:

JDS Labs Element DAC, USB Audio
Direct hardware device without any conversions

Supported Formats:

S16, S24_3

----------------------------------------

Device:

hw:CARD=DAC,DEV=1

Description:

JDS Labs Element DAC, USB Audio #1
Direct hardware device without any conversions

Supported Formats:

S16

----------------------------------------

Device:

plughw:CARD=DAC,DEV=0

Description:

JDS Labs Element DAC, USB Audio
Hardware device with all software conversions

Supported Formats:

S16, S24, S24_3, S24_3, S32, F32, F64

----------------------------------------

Device:

plughw:CARD=DAC,DEV=1

Description:

JDS Labs Element DAC, USB Audio #1
Hardware device with all software conversions

Supported Formats:

S16, S24, S24_3, S24_3, S32, F32, F64

----------------------------------------

Device:

sysdefault:CARD=DAC

Description:

JDS Labs Element DAC, USB Audio
Default Audio Device

Supported Formats:

S16, S24, S24_3, S24_3, S32, F32, F64

----------------------------------------

I actually like this better than trying to emulate ALSA. It only gives the user useful info. It would not show devices that can't do 2 ch 44.1 Interleaved.

fn list_outputs() -> SinkResult<()> {
    println!("\nCompatible alsa devices:\n");
    println!("----------------------------------------\n");

    let i = HintIter::new_str(None, "pcm").map_err(|_| AlsaError::Parsing)?;

    for a in i {
        if let Some(Direction::Playback) = a.direction {
            let name = a.name.ok_or(AlsaError::Parsing)?;
            let desc = a.desc.ok_or(AlsaError::Parsing)?;

            if let Ok(pcm) = PCM::new(&name, Direction::Playback, false) {
                if let Ok(hwp) = HwParams::any(&pcm) {
                    // Only show devices that support
                    // 2 ch 44.1 Interleaved.
                    if hwp.test_rate(SAMPLE_RATE).is_ok()
                            && hwp.test_channels(NUM_CHANNELS as u32).is_ok()
                            // There is no `test_access` in the bindings.
                            && hwp.set_access(Access::RWInterleaved).is_ok()
                    {
                        println!("Device:\n\n{}\n", name);
                        println!("Description:\n\n{}\n", desc);

                        let mut supported_formats = Vec::new();

                        for f in [
                            Format::s16(),
                            Format::s24(),
                            Format::S243LE,
                            Format::S243BE,
                            Format::s32(),
                            Format::float(),
                            Format::float64(),
                        ] {
                            if hwp.test_format(f).is_ok() {
                                let f = match f {
                                    Format::Float64LE | Format::Float64BE => AudioFormat::F64,
                                    Format::FloatLE | Format::FloatBE => AudioFormat::F32,
                                    Format::S32LE | Format::S32BE => AudioFormat::S32,
                                    Format::S24LE | Format::S24BE => AudioFormat::S24,
                                    Format::S243LE | Format::S243BE => AudioFormat::S24_3,
                                    Format::S16LE | Format::S16BE => AudioFormat::S16,
                                    _ => unreachable!(),
                                };

                                supported_formats.push(format!("{:?}", f));
                            }
                        }
                        println!("Supported Formats:\n\n{}\n", supported_formats.join(", "));
                        println!("----------------------------------------\n");
                    }
                };
            }
        }
    }

    Ok(())
}

[roderickvd]

If I understand correctly, you are suggesting to enhance the existing command-line --device ? option and have it report capabilities that are useful to librespot. I agree that that'd be something nice to have.

[JasonLG1979]

Yes. Basically instead of showing the user a bunch of devices that may not be compatible and a bunch of extraneous info, just show useful info.

[roderickvd]

OK let's continue at #883.

[JasonLG1979]

OK