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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"alsa_volume.py: get_state() reads Capture volume instead of Playback on mixed-channel mixer elements","articleBody":"  On USB DACs where the ALSA mixer element exposes both Capture and Playback channels (e.g. CX31993+MAX97220 Headset element), AlsaVolumeController.get_state() returns the wrong volume.                                                                 \n                                                                                                                                                                                                                                                          \n  Root cause:\n\n  get_state() runs amixer -M -c \u003ccard> sget \u003celement> and searches the full output with _VOLUME_RE.search(output), which matches the first [XX%] it finds. On the CX31993+MAX97220, the Headset element outputs Capture before Playback:\n\n```\n  Simple mixer control 'Headset',0\n    Capabilities: pvolume cvolume cvolume-joined pswitch pswitch-joined cswitch cswitch-joined\n    Playback channels: Front Left - Front Right\n    Capture channels: Mono\n    Limits: Playback 0 - 148 Capture 0 - 148\n    Mono: Capture 140 [85%] [-4.00dB] [on]\n    Front Left: Playback 75 [20%] [-36.50dB] [off]\n    Front Right: Playback 75 [20%] [-36.50dB] [off]\n```\n\n  The regex matches [85%] (Capture/mic input) instead of [20%] (Playback). The same issue affects the mute switch detection — it reads Capture [on] instead of Playback [off].\n\n  Impact:\n\n  When MA calls _refresh_client_info() on sync group playback start, it reads get_player_volume() from each client. Affected clients report 85% (the Capture value), and MA overwrites their tracked volume. The sync leader (which may use a different\n  DAC without this issue) keeps its correct volume, but all affected followers jump to 85%.\n\n  set_state() is not affected — it correctly targets playback explicitly in the amixer command.\n\n  Test data:\n\n  The amixer -M output above can be used as a test fixture to verify the fix. Expected parse result should be volume=20, muted=True (from the Playback lines), not volume=85, muted=False (from the Capture line).\n\n  Suggested fix:\n\n  Replace get_state() in AlsaVolumeController with:\n\n  async def get_state(self) -> tuple[int, bool]:\n      \"\"\"Read ALSA mixer volume and mute state.\"\"\"\n      proc = await asyncio.create_subprocess_exec(\n          \"amixer\",\n          \"-M\",\n          \"-c\",\n          self._card,\n          \"sget\",\n          self._element,\n          stdout=asyncio.subprocess.PIPE,\n          stderr=asyncio.subprocess.PIPE,\n      )\n      stdout, stderr = await proc.communicate()\n      if proc.returncode != 0:\n          raise RuntimeError(\n              f\"amixer sget failed (exit {proc.returncode}): \"\n              f\"{stderr.decode().strip() if stderr else '(empty)'}\"\n          )\n\n      output = stdout.decode()\n\n      # Filter for Playback lines to avoid matching Capture channel values\n      # on mixer elements that expose both (e.g. CX31993+MAX97220 Headset).\n      # Falls back to full output for elements without separate Playback lines.\n      playback_lines = [l for l in output.splitlines() if \"Playback\" in l and \"%\" in l]\n      vol_match = (\n          _VOLUME_RE.search(playback_lines[0])\n          if playback_lines\n          else _VOLUME_RE.search(output)\n      )\n\n      playback_switch_lines = [l for l in output.splitlines() if \"Playback\" in l and \"[o\" in l]\n      switch_match = (\n          _SWITCH_RE.search(playback_switch_lines[0])\n          if playback_switch_lines\n          else _SWITCH_RE.search(output)\n      )\n\n      if vol_match is None:\n          raise RuntimeError(f\"Could not parse volume from amixer output: {output!r}\")\n\n      volume = int(vol_match.group(1))\n      muted = switch_match.group(1) == \"off\" if switch_match else False\n      return volume, muted\n\n  Affected hardware: Any ALSA mixer element with both Capture and Playback channels where Capture appears first in amixer output. Confirmed on CX31993+MAX97220 USB DAC (Headset element).","author":{"url":"https://github.com/1liminal1","@type":"Person","name":"1liminal1"},"datePublished":"2026-04-28T02:02:38Z","url":"https://github.com/Sendspin/sendspin-python-cli/issues/236"}