fixup! Implement a decoder

Consistent use of av_image_get_linesize

Author: lookback-hugotunius

src/decoder.rs

@@ -293,7 +293,18 @@ impl FrameRef for DecodedFrame {
         assert!(i < sys::AV_NUM_DATA_POINTERS as usize);
 
         // SAFETY: The pointer is valid while self is alive.
-        unsafe { (*self.0).linesize[i] as usize }
+        unsafe {
+            assert_eq!(
+                (*self.0).format,
+                PixelFormat::AV_PIX_FMT_YUV420P as i32,
+                "Only YUV420P is supported"
+            );
+            sys::av_image_get_linesize(
+                PixelFormat::AV_PIX_FMT_YUV420P,
+                self.width() as i32,
+                i as i32,
+            ) as usize
+        }
     }
 }