fix: make !volume apply immediately during playback

stream_audio now accepts a callable for volume, re-read on each PCM
frame instead of capturing a static float at track start.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/CHEATSHEET.md

@@ -556,8 +556,8 @@ HTML stripped on receive, escaped on send. IRC-only commands are no-ops.
 !volume 75               # Set volume (0-100, default 50)
 ```
 
-Requires: `yt-dlp`, `ffmpeg`, `libopus.so.0` on the host.
+Requires: `yt-dlp`, `ffmpeg`, `libopus` on the host.
-Max 50 tracks in queue. Volume applies on next track.
+Max 50 tracks in queue. Volume changes take effect immediately.
 Mumble-only: `!play` replies with error on other adapters, others silently no-op.
 
 ## Plugin Template

docs/USAGE.md

@@ -1576,7 +1576,7 @@ and voice transmission.
 ```
 
 - Queue holds up to 50 tracks
-- Volume applies from the next track (default: 50%)
+- Volume takes effect immediately during playback (default: 50%)
 - Title resolved via `yt-dlp --get-title` before playback
 - Audio pipeline: `yt-dlp | ffmpeg` subprocess, PCM fed to pymumble
 - Commands are Mumble-only; `!play` on other adapters replies with an error,

plugins/music.py

@@ -78,10 +78,11 @@ async def _play_loop(bot) -> None:
             done = asyncio.Event()
             ps["done_event"] = done
 
-            volume = ps["volume"] / 100.0
             try:
                 await bot.stream_audio(
-                    track.url, volume=volume, on_done=done,
+                    track.url,
+                    volume=lambda: ps["volume"] / 100.0,
+                    on_done=done,
                 )
             except asyncio.CancelledError:
                 raise
@@ -269,7 +270,7 @@ async def cmd_volume(bot, message):
 
     Usage:
         !volume         Show current volume
-        !volume <0-100> Set volume (applies on next track)
+        !volume <0-100> Set volume (takes effect immediately)
     """
     if not _is_mumble(bot):
         return

src/derp/mumble.py

@@ -421,7 +421,7 @@ class MumbleBot:
         self,
         url: str,
         *,
-        volume: float = 0.5,
+        volume=0.5,
         on_done=None,
     ) -> None:
         """Stream audio from URL through yt-dlp|ffmpeg to voice channel.
@@ -432,12 +432,16 @@ class MumbleBot:
 
         Feeds raw PCM to pymumble's sound_output which handles Opus
         encoding, packetization, and timing.
+
+        ``volume`` may be a float (static) or a callable returning float
+        (dynamic, re-read each frame).
         """
         if self._mumble is None:
             return
 
+        _get_vol = volume if callable(volume) else lambda: volume
         log.info("stream_audio: starting pipeline for %s (vol=%.0f%%)",
-                 url, volume * 100)
+                 url, _get_vol() * 100)
 
         proc = await asyncio.create_subprocess_exec(
             "sh", "-c",
@@ -457,8 +461,9 @@ class MumbleBot:
                 if len(pcm) < _FRAME_BYTES:
                     pcm += b"\x00" * (_FRAME_BYTES - len(pcm))
 
-                if volume != 1.0:
+                vol = _get_vol()
-                    pcm = _scale_pcm(pcm, volume)
+                if vol != 1.0:
+                    pcm = _scale_pcm(pcm, vol)
 
                 self._mumble.sound_output.add_sound(pcm)
                 frames += 1