add SharedMemoryWriter support - without gstreamer

docs/SOCKET_API.md

@@ -600,10 +600,14 @@ Retrieve all current eHDR settings.
 
 ### 21. Enable Shared Memory
 
-Enable shared memory output for direct frame access by external processes. This creates a shared memory region at `/dev/shm/<name>` where frames are written in parallel to the GStreamer pipeline.
+Enable shared memory output for direct frame access by external processes. This creates a shared memory region at `/dev/shm/<name>` where frames are written.
 
 **Note:** Cannot be enabled while streaming is active. Must be enabled before starting the stream.
 
+**Important:** Shared memory can be used **with or without** GStreamer:
+- **With GStreamer:** Frames are written to both GStreamer pipeline and shared memory
+- **Without GStreamer:** Set pipeline to empty string `""` - frames are only written to shared memory
+
 **Command:**
 ```json
 {
@@ -698,7 +702,7 @@ Query the current shared memory configuration.
 
 ## Usage Examples
 
-### Complete Workflow Example
+### Complete Workflow Example (GStreamer + Shared Memory)
 
 ```bash
 # 1. Set GStreamer pipeline for UDP streaming
@@ -721,7 +725,7 @@ echo '{"command":"set_ehdr_ratio_max","params":{"value":"24"}}' | socat - UNIX-C
 # 3b. (Optional) Enable shared memory output
 echo '{"command":"enable_shared_memory","params":{"name":"/vizion_frame","buffer_size":"8294528"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
 
-# 4. Start streaming
+# 4. Start streaming (both GStreamer and shared memory active)
 echo '{"command":"start_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
 
 # 5. Check status
@@ -735,6 +739,36 @@ echo '{"command":"stop_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
 echo '{"command":"disable_shared_memory"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
 ```
 
+### Shared Memory Only Workflow (No GStreamer)
+
+```bash
+# 1. Disable GStreamer pipeline
+echo '{"command":"set_pipeline","params":{"pipeline":""}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 2. Set video format
+echo '{"command":"set_format","params":{"width":"1920","height":"1080","framerate":"30","format":"YUY2"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 3. Configure camera settings
+echo '{"command":"set_exposure","params":{"mode":"auto"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+echo '{"command":"set_brightness","params":{"value":"50"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 4. Enable shared memory
+echo '{"command":"enable_shared_memory","params":{"name":"/vizion_frame","buffer_size":"8294528"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 5. Start streaming (shared memory only)
+echo '{"command":"start_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+# Output: "GStreamer pipeline disabled (using shared memory only)"
+
+# 6. Check that shared memory is being updated
+ls -l /dev/shm/vizion_frame  # Watch file modification time
+
+# 7. Stop streaming
+echo '{"command":"stop_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 8. Disable shared memory
+echo '{"command":"disable_shared_memory"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+```
+
 ### GStreamer Pipeline Examples
 
 ```bash
@@ -819,6 +853,35 @@ ls -lh /dev/shm/vizion_frame
 watch -n 0.1 'ls -l /dev/shm/vizion_frame'
 ```
 
+### Shared Memory WITHOUT GStreamer (Shared Memory Only)
+
+To use shared memory without GStreamer, disable the GStreamer pipeline by setting it to an empty string:
+
+```bash
+# 1. Disable GStreamer pipeline
+echo '{"command":"set_pipeline","params":{"pipeline":""}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 2. Enable shared memory
+echo '{"command":"enable_shared_memory","params":{"name":"/vizion_frame","buffer_size":"8294528"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 3. Start streaming (frames will only go to shared memory)
+echo '{"command":"start_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# Output: "GStreamer pipeline disabled (using shared memory only)"
+
+# 4. Stop streaming
+echo '{"command":"stop_stream"}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+
+# 5. Optionally re-enable GStreamer for next session
+echo '{"command":"set_pipeline","params":{"pipeline":"videoconvert ! autovideosink"}}' | socat - UNIX-CONNECT:/tmp/vizion_control.sock
+```
+
+**Benefits of Shared Memory Only Mode:**
+- Lower CPU usage (no GStreamer overhead)
+- Lower memory bandwidth (no duplicate frame copies to GStreamer)
+- Suitable for headless systems or custom processing pipelines
+- Multiple external processes can still read from shared memory simultaneously
+
 ### Using `nc` (netcat with Unix socket support)
 
 ```bash
@@ -864,7 +927,7 @@ print(send_command("set_ehdr_ratio_min", {"value": "12"}))
 print(send_command("set_ehdr_ratio_max", {"value": "24"}))
 print(send_command("get_ehdr_status"))  # Get current eHDR settings
 
-# Shared memory control examples
+# Shared memory control examples (with GStreamer)
 print(send_command("enable_shared_memory", {
     "name": "/vizion_frame",
     "buffer_size": "8294528"
@@ -874,6 +937,17 @@ print(send_command("start_stream"))
 # ... streaming active, external process can read /dev/shm/vizion_frame ...
 print(send_command("stop_stream"))
 print(send_command("disable_shared_memory"))
+
+# Shared memory only (without GStreamer)
+print(send_command("set_pipeline", {"pipeline": ""}))  # Disable GStreamer
+print(send_command("enable_shared_memory", {
+    "name": "/vizion_frame",
+    "buffer_size": "8294528"
+}))
+print(send_command("start_stream"))  # Frames only go to shared memory
+# Output: "GStreamer pipeline disabled (using shared memory only)"
+print(send_command("stop_stream"))
+print(send_command("disable_shared_memory"))
 ```
 
 ### Using C++
@@ -915,7 +989,7 @@ int main() {
     std::cout << sendCommand(R"({"command":"set_ehdr_exposure_max","params":{"value":"4"}})") << std::endl;
     std::cout << sendCommand(R"({"command":"get_ehdr_status"})") << std::endl;
 
-    // Shared memory control examples
+    // Shared memory control examples (with GStreamer)
     std::cout << sendCommand(R"({"command":"enable_shared_memory","params":{"name":"/vizion_frame","buffer_size":"8294528"}})") << std::endl;
     std::cout << sendCommand(R"({"command":"get_shared_memory_status"})") << std::endl;
     std::cout << sendCommand(R"({"command":"start_stream"})") << std::endl;
@@ -923,6 +997,14 @@ int main() {
     std::cout << sendCommand(R"({"command":"stop_stream"})") << std::endl;
     std::cout << sendCommand(R"({"command":"disable_shared_memory"})") << std::endl;
 
+    // Shared memory only (without GStreamer)
+    std::cout << sendCommand(R"({"command":"set_pipeline","params":{"pipeline":""}})") << std::endl;  // Disable GStreamer
+    std::cout << sendCommand(R"({"command":"enable_shared_memory","params":{"name":"/vizion_frame","buffer_size":"8294528"}})") << std::endl;
+    std::cout << sendCommand(R"({"command":"start_stream"})") << std::endl;  // Frames only go to shared memory
+    // Output: "GStreamer pipeline disabled (using shared memory only)"
+    std::cout << sendCommand(R"({"command":"stop_stream"})") << std::endl;
+    std::cout << sendCommand(R"({"command":"disable_shared_memory"})") << std::endl;
+
     return 0;
 }
 ```
@@ -1316,7 +1398,11 @@ finally:
 - Default pipeline: `videoconvert ! autovideosink` (display locally)
 - eHDR features require compatible camera models (VCI/VCS/VLS3/VLS-GM2/TEVS-AR0821/AR0822)
 - eHDR settings may be reset to defaults when the camera starts streaming (driver behavior)
-- Shared memory output is independent of GStreamer pipeline (both run in parallel)
+- Shared memory output can run with or without GStreamer pipeline:
+  - **With GStreamer:** Both outputs active (parallel operation)
+  - **Without GStreamer:** Set pipeline to `""` for shared memory only (lower CPU/memory usage)
 - Shared memory must be enabled before starting the stream
+- At least one output (GStreamer or shared memory) must be configured to start streaming
 - Shared memory files are automatically cleaned up when disabled or on clean exit
 - Multiple processes can read from the same shared memory region simultaneously
+- Shared memory only mode is recommended for headless systems or custom processing applications

src/StreamingEngine.cpp

@@ -35,8 +35,14 @@ bool StreamingEngine::start(const std::string& gstPipeline) {
         return false;
     }
 
-    // Set pipeline description
+    // Check if at least one output is configured
-    gstPipeline_->setPipelineDescription(gstPipeline);
+    const bool useGStreamer = !gstPipeline.empty();
+    const bool useSharedMemory = (shmWriter_ && shmWriter_->isCreated());
+
+    if (!useGStreamer && !useSharedMemory) {
+        std::cerr << "No output configured. Enable GStreamer pipeline or shared memory first." << std::endl;
+        return false;
+    }
 
     // Start camera streaming
     if (VxStartStreaming(camera_) != 0) {
@@ -58,11 +64,17 @@ bool StreamingEngine::start(const std::string& gstPipeline) {
     bufferSize_ = calculatedBufferSize;
     buffer_ = std::make_unique<uint8_t[]>(bufferSize_);
 
-    // Start GStreamer pipeline
+    // Start GStreamer pipeline if configured
-    if (!gstPipeline_->start()) {
+    if (useGStreamer) {
-        std::cerr << "Failed to start GStreamer pipeline" << std::endl;
+        gstPipeline_->setPipelineDescription(gstPipeline);
-        VxStopStreaming(camera_);
+        if (!gstPipeline_->start()) {
-        return false;
+            std::cerr << "Failed to start GStreamer pipeline" << std::endl;
+            VxStopStreaming(camera_);
+            return false;
+        }
+        std::cout << "GStreamer pipeline started" << std::endl;
+    } else {
+        std::cout << "GStreamer pipeline disabled (using shared memory only)" << std::endl;
     }
 
     // Start acquisition thread
@@ -85,8 +97,10 @@ void StreamingEngine::stop() {
         acquisitionThread_->join();
     }
 
-    // Stop GStreamer pipeline
+    // Stop GStreamer pipeline if running
-    gstPipeline_->stop();
+    if (gstPipeline_->isRunning()) {
+        gstPipeline_->stop();
+    }
 
     // Stop camera streaming
     VxStopStreaming(camera_);
@@ -131,11 +145,13 @@ void StreamingEngine::acquisitionLoop() {
                 default: formatStr = "UNKNOWN"; break;
             }
 
-            // Push frame to GStreamer pipeline
+            // Push frame to GStreamer pipeline if active
-            if (!gstPipeline_->pushBuffer(buffer_.get(), dataSize,
+            if (gstPipeline_->isRunning()) {
-                                         currentFormat_.width, currentFormat_.height,
+                if (!gstPipeline_->pushBuffer(buffer_.get(), dataSize,
-                                         formatStr)) {
+                                             currentFormat_.width, currentFormat_.height,
-                std::cerr << "Failed to push frame to GStreamer pipeline" << std::endl;
+                                             formatStr)) {
+                    std::cerr << "Failed to push frame to GStreamer pipeline" << std::endl;
+                }
             }
 
             // Push frame to shared memory if enabled