AlexxIT/go2rtc · error

[alsa] set sw_params

Error message

[alsa] set sw_params: %w

What it means

The SNDRV_PCM_IOCTL_SW_PARAMS ioctl failed while applying software parameters (period step, avail_min, start/stop thresholds) to the ALSA PCM device. Wraps the kernel errno; usually the software params are inconsistent with previously set hardware params. Called by Start and AddTrack.

Solutions

  1. Retry after re-negotiating hardware params
  2. Verify the device is not busy or in an invalid state (restart the stream)
  3. Check dmesg for ALSA driver errors
Defensive patterns

Strategy: retry

When it happens

Trigger: Thrown at pkg/alsa/device/device_linux.go:159 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of AlexxIT/go2rtc@c245815e75 (2026-09-07). Data as JSON: /api/errors/0ec5cb71e2f95e39. Report an issue: GitHub.

Appendix: source

Thrown at pkg/alsa/device/device_linux.go:159

	_, periods := d.getInterval(SNDRV_PCM_HW_PARAM_PERIODS)
	_, periodSize := d.getInterval(SNDRV_PCM_HW_PARAM_PERIOD_SIZE)
	threshold := snd_pcm_uframes_t(periods * periodSize) // same as bufferSize

	swparams := snd_pcm_sw_params{
		//tstamp_mode: SNDRV_PCM_TSTAMP_ENABLE,
		period_step:    1,
		avail_min:      1, // start as soon as possible
		stop_threshold: threshold,
	}

	if d.IsCapture() {
		swparams.start_threshold = 1
	} else {
		swparams.start_threshold = threshold
	}

	if err := ioctl(d.fd, SNDRV_PCM_IOCTL_SW_PARAMS, &swparams); err != nil {
		return fmt.Errorf("[alsa] set sw_params: %w", err)
	}

	if err := ioctl(d.fd, SNDRV_PCM_IOCTL_PREPARE, nil); err != nil {
		return fmt.Errorf("[alsa] prepare: %w", err)
	}

	return nil
}

func (d *Device) Write(b []byte) (n int, err error) {
	xfer := &snd_xferi{
		buf:    uintptr(unsafe.Pointer(&b[0])),
		frames: snd_pcm_uframes_t(len(b) / d.frameBytes),
	}
	err = ioctl(d.fd, SNDRV_PCM_IOCTL_WRITEI_FRAMES, xfer)
	if err == syscall.EPIPE {
		// auto handle underrun state
		// https://stackoverflow.com/questions/59396728/how-to-properly-handle-xrun-in-alsa-programming-when-playing-audio-with-snd-pcm

View on GitHub (pinned to c245815e75)