Add environment variable for overriding decoder capabilities

app/streaming/video/ffmpeg.cpp

@@ -70,7 +70,17 @@ void FFmpegVideoDecoder::setHdrMode(bool enabled)
 
 int FFmpegVideoDecoder::getDecoderCapabilities()
 {
-    int capabilities = m_BackendRenderer->getDecoderCapabilities();
+    bool ok;
+
+    int capabilities = qEnvironmentVariableIntValue("DECODER_CAPS", &ok);
+    if (ok) {
+        SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
+                    "Using decoder capability override: 0x%x",
+                    capabilities);
+    }
+    else {
+        // Start with the backend renderer's capabilities
+        capabilities = m_BackendRenderer->getDecoderCapabilities();
 
         if (!isHardwareAccelerated()) {
             // Slice up to 4 times for parallel CPU decoding, once slice per core
@@ -80,8 +90,11 @@ int FFmpegVideoDecoder::getDecoderCapabilities()
                         slices);
             capabilities |= CAPABILITY_SLICES_PER_FRAME(slices);
         }
+    }
 
-    // We use our own decoder thread with the "pull" model
+    // We use our own decoder thread with the "pull" model. This cannot
+    // be overridden using the by the user because it is critical to
+    // our operation.
     capabilities |= CAPABILITY_PULL_RENDERER;
 
     return capabilities;