GPU3: GPU export rendering off by default until it is faster (#30)

Set GpuRendering default to Off in ExportSettings so exports use the CPU
reference renderer by default until GPU export achieves lower wall-clock time.

🤖 Written by agy (Antigravity Agent, Gemini 3.8 Flash)

crates/export/src/lib.rs

@@ -458,7 +458,7 @@ impl Default for ExportSettings {
             h264_level: None,
             bitrate_mode: BitrateMode::default(),
             hardware_encoding: HardwareEncoding::default(),
-            gpu_rendering: GpuRendering::Auto,
+            gpu_rendering: GpuRendering::Off,
             max_bitrate_kbps: None,
             adaptive_bitrate: None,
             keyframe_distance: None,

crates/export/src/settings.rs

@@ -78,12 +78,12 @@ pub enum HardwareEncoding {
 /// Whether the picture of an export may be composited on the GPU (`filmcraft-gpu`'s off-screen
 /// compositor) instead of the CPU reference renderer. Auto = use the GPU when the app registered
 /// a GPU frame renderer and the machine has an adapter; the CPU result is the fallback either
-/// way. Off = today's CPU behaviour exactly.
+/// way. Off = today's CPU behaviour exactly (default until GPU export is faster than CPU export).
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub enum GpuRendering {
-    #[default]
     Auto,
+    #[default]
     Off,
 }