[obs] audio: capture guest playback

Subscribe the OBS source as a playback-only LGMP audio client. Decode
the advertised formats and channel maps, then resample into the OBS
clock domain without participating in driver clock feedback.

Keep queue and resampler storage fixed in the packet path.

obs/CMakeLists.txt

@@ -8,6 +8,8 @@ include(CheckSubmodule)
 include(GNUInstallDirs)
 include(CheckCCompilerFlag)
 include(FeatureSummary)
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(SAMPLERATE REQUIRED IMPORTED_TARGET samplerate)
 
 set(OPTIMIZE_FOR_NATIVE_DEFAULT ON)
 include(OptimizeForNative) # option(OPTIMIZE_FOR_NATIVE)
@@ -104,6 +106,7 @@ link_libraries(
 
 set(SOURCES
   ${CMAKE_BINARY_DIR}/version.c
+  audio.c
   frame_scheduler.c
   main.c
   lg.c
@@ -120,6 +123,7 @@ target_link_libraries(looking-glass-obs
   ${EXE_FLAGS}
   lg_common
   lgmp
+  PkgConfig::SAMPLERATE
 )
 
 install(TARGETS looking-glass-obs

obs/audio.h

@@ -0,0 +1,49 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef LG_OBS_AUDIO_H
+#define LG_OBS_AUDIO_H
+
+#include <obs/obs.h>
+
+#include <LGProtocol/KVMFRAudio.h>
+#include <lgmp/client.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct LGOBSAudio LGOBSAudio;
+
+bool lgObsAudioCreate(LGOBSAudio ** result, obs_source_t * source);
+void lgObsAudioDestroy(LGOBSAudio ** audio);
+
+bool lgObsAudioConnect(LGOBSAudio * audio, PLGMPClient client,
+    uint32_t clientID);
+void lgObsAudioPumpPointer(LGOBSAudio * audio,
+    PLGMPClientQueue pointerQueue);
+void lgObsAudioHandleResponse(LGOBSAudio * audio,
+    const KVMFRAudioStreamResponse * response);
+
+void lgObsAudioSetEnabled(LGOBSAudio * audio, bool enabled);
+void lgObsAudioSetActive(LGOBSAudio * audio, bool active);
+void lgObsAudioDisconnect(LGOBSAudio * audio);
+
+#endif

obs/lg.c

@@ -42,6 +42,7 @@
 #include "hdrpq.effect.h"
 #include "cursor.effect.h"
 #include "frame_scheduler.h"
+#include "audio.h"
 
 #define LG_FRAME_TIMING_SPIN_COUNT 4096
 
@@ -136,6 +137,7 @@ typedef struct
   pthread_mutex_t      pointerLock;
   LGFrameScheduler     frameScheduler;
   _Atomic(bool)        sourceActive;
+  LGOBSAudio         * audio;
 
   bool                 cursorMono;
   gs_texture_t       * cursorTex;
@@ -439,6 +441,20 @@ static void * lgCreate(obs_data_t * settings, obs_source_t * context)
   atomic_store(&this->cursorTransformVer, 0);
   atomic_store(&this->sdrWhiteLevel, KVMFR_SDR_WHITE_LEVEL_DEFAULT);
   atomic_store(&this->sourceActive, obs_source_active(context));
+  if (!lgObsAudioCreate(&this->audio, context))
+  {
+    blog(LOG_ERROR, "Failed to initialize Looking Glass audio");
+    os_sem_destroy(this->frameSem);
+    os_sem_destroy(this->cursorSem);
+    pthread_mutex_destroy(&this->pointerLock);
+    obs_enter_graphics();
+    gs_effect_destroy(this->unpackEffect);
+    gs_effect_destroy(this->hdrEffect);
+    gs_effect_destroy(this->cursorEffect);
+    obs_leave_graphics();
+    bfree(this);
+    return NULL;
+  }
   lgUpdate(this, settings);
   return this;
 }
@@ -514,6 +530,7 @@ static void dmabufReset(LGPlugin * this)
 
 static void deinit(LGPlugin * this)
 {
+  lgObsAudioDisconnect(this->audio);
   bool closeShm = false;
   switch(this->state)
   {
@@ -610,6 +627,7 @@ static void lgDestroy(void * data)
 {
   LGPlugin * this = (LGPlugin *)data;
   deinit(this);
+  lgObsAudioDestroy(&this->audio);
   os_sem_destroy(this->frameSem );
   os_sem_destroy(this->cursorSem);
   pthread_mutex_destroy(&this->pointerLock);
@@ -626,6 +644,7 @@ static void lgDestroy(void * data)
 static void lgGetDefaults(obs_data_t * defaults)
 {
   obs_data_set_default_string(defaults, "shmFile", "/dev/kvmfr0");
+  obs_data_set_default_bool(defaults, "captureAudio", true);
 #if LIBOBS_API_MAJOR_VER >= 27
   obs_data_set_default_bool(defaults, "dmabuf", true);
 #endif
@@ -639,6 +658,8 @@ static obs_properties_t * lgGetProperties(void * data)
       obs_module_text("SHM File"), OBS_TEXT_DEFAULT);
   obs_properties_add_bool(props, "hideMouse",
       obs_module_text("Hide mouse cursor"));
+  obs_properties_add_bool(props, "captureAudio",
+      obs_module_text("Capture guest audio"));
 #if LIBOBS_API_MAJOR_VER >= 27
   obs_properties_add_bool(props, "dmabuf",
       obs_module_text("Use DMABUF import (requires kvmfr device)"));
@@ -771,6 +792,7 @@ static void * pointerThread(void * data)
     LGMPMessage msg;
 
     pthread_mutex_lock(&this->pointerLock);
+    lgObsAudioPumpPointer(this->audio, this->pointerQueue);
     if ((status = lgmpClientProcess(this->pointerQueue, &msg)) != LGMP_OK)
     {
       pthread_mutex_unlock(&this->pointerLock);
@@ -784,6 +806,31 @@ static void * pointerThread(void * data)
       continue;
     }
 
+    const uint32_t pointerTag = (uint32_t)(msg.udata >> 32);
+    if (pointerTag)
+    {
+      KVMFRAudioStreamResponse response;
+      const bool audioResponse =
+        pointerTag == KVMFR_AUDIO_CONTROL_TAG;
+      const bool valid = audioResponse &&
+        msg.udata == KVMFR_AUDIO_CONTROL_UDATA &&
+        msg.mem && msg.size == sizeof(response);
+      if (valid)
+        memcpy(&response, msg.mem, sizeof(response));
+      status = lgmpClientMessageDone(this->pointerQueue);
+      pthread_mutex_unlock(&this->pointerLock);
+      if (status != LGMP_OK)
+      {
+        printf("lgmpClientMessageDone: %s\n", lgmpStatusString(status));
+        break;
+      }
+      if (valid)
+        lgObsAudioHandleResponse(this->audio, &response);
+      else if (audioResponse)
+        blog(LOG_WARNING, "Ignoring malformed Looking Glass audio response");
+      continue;
+    }
+
     const KVMFRCursor * const cursor = (const KVMFRCursor * const)msg.mem;
     if (msg.udata & CURSOR_FLAG_VISIBLE_VALID)
     {
@@ -920,6 +967,8 @@ static void lgUpdate(void * data, obs_data_t * settings)
   LGPlugin * this = (LGPlugin *)data;
 
   deinit(this);
+  lgObsAudioSetEnabled(this->audio,
+      obs_data_get_bool(settings, "captureAudio"));
   this->shmFile = bstrdup(obs_data_get_string(settings, "shmFile"));
   if (!ivshmemOpenDev(&this->shmDev, this->shmFile))
     return;
@@ -974,6 +1023,9 @@ static void lgUpdate(void * data, obs_data_t * settings)
 
   lgFrameSchedulerInit(&this->frameScheduler,
     udata->features & KVMFR_FEATURE_FRAME_SCHEDULE, clientID);
+  if ((udata->features & KVMFR_FEATURE_AUDIO) &&
+      !lgObsAudioConnect(this->audio, this->lgmp, clientID))
+    blog(LOG_WARNING, "Failed to connect Looking Glass audio transport");
 
   this->state = STATE_STARTING;
   createThreads(this);
@@ -1738,6 +1790,7 @@ static void lgActivate(void * data)
   LGPlugin * this = (LGPlugin *)data;
   atomic_store_explicit(
     &this->sourceActive, true, memory_order_release);
+  lgObsAudioSetActive(this->audio, true);
 }
 
 static void lgDeactivate(void * data)
@@ -1745,6 +1798,7 @@ static void lgDeactivate(void * data)
   LGPlugin * this = (LGPlugin *)data;
   atomic_store_explicit(
     &this->sourceActive, false, memory_order_release);
+  lgObsAudioSetActive(this->audio, false);
 }
 
 static void lgSetupCursorEffect(LGPlugin * this, int outputTransfer)
@@ -1931,7 +1985,8 @@ struct obs_source_info lg_source =
 {
   .id                    = "looking-glass-obs",
   .type                  = OBS_SOURCE_TYPE_INPUT,
-  .output_flags          = OBS_SOURCE_VIDEO | OBS_SOURCE_CUSTOM_DRAW |
+  .output_flags          = OBS_SOURCE_VIDEO | OBS_SOURCE_AUDIO |
+                           OBS_SOURCE_CUSTOM_DRAW |
                            OBS_SOURCE_DO_NOT_DUPLICATE | OBS_SOURCE_SRGB,
   .get_name              = lgGetName,
   .create                = lgCreate,