🐛(frontend) fix dimension mismatch in BackgroundCustomProcessor

The getImageData call was using PROCESSING_WIDTH for both dimensions
instead of PROCESSING_WIDTH and PROCESSING_HEIGHT. This caused the
source image data to be 256x256 instead of the expected 256x144, leading
to buffer overflow when writing to the segmentation mask and potential
visual artifacts in Firefox background effects.

CHANGELOG.md

@@ -37,6 +37,10 @@ and this project adheres to
 - 🐛(backend) refactor lobby throttling to use participant id #1129
 - 🩹(backend) ignore non-recording uploads in storage webhook handler #1142
 
+### Fixed
+
+- 🐛(frontend) fix dimension mismatch in BackgroundCustomProcessor getImageData #1116
+
 ## [1.10.0] - 2026-03-05
 
 ### Changed

src/frontend/src/features/rooms/livekit/components/blur/BackgroundCustomProcessor.ts

@@ -187,7 +187,7 @@ export class BackgroundCustomProcessor implements BackgroundProcessorInterface {
       0,
       0,
       PROCESSING_WIDTH,
-      PROCESSING_WIDTH
+      PROCESSING_HEIGHT
     )
   }