fix(android): improve error handling for external storage file access

.changes/android-external-files-fix.md

@@ -0,0 +1,5 @@
+---
+"tauri": patch:bug
+---
+
+Fixed 500 error when accessing local video files in Android external storage directory via `convertFileSrc`. Added better error handling and logging for Android external storage access to help diagnose permission and accessibility issues.

crates/tauri/src/protocol/asset.rs

@@ -48,8 +48,31 @@ fn get_response(
     return resp.status(403).body(Vec::new().into()).map_err(Into::into);
   }
 
+  // Check if the file exists before trying to open it
+  if !std::path::Path::new(&path).exists() {
+    log::error!("File does not exist at path: {}", path);
+    return resp.status(404).body(Vec::new().into()).map_err(Into::into);
+  }
+
+  // Check if we have read permissions
+  if let Err(e) = std::fs::metadata(&path) {
+    log::error!("Failed to get metadata for {}: {}", path, e);
+    return resp.status(422).body(format!("Failed to access file metadata: {}", e).into_bytes().into()).map_err(Into::into);
+  }
+
   let (mut file, len, mime_type, read_bytes) = crate::async_runtime::safe_block_on(async move {
-    let mut file = File::open(&path).await?;
+    let mut file = match File::open(&path).await {
+      Ok(file) => file,
+      Err(e) => {
+        #[cfg(target_os = "android")]
+        {
+          if path.starts_with("/storage/emulated/0/Android/data/") {
+            log::error!("Failed to open Android external storage file '{}': {}. This may be due to missing storage permissions or the file being inaccessible from the webview context.", path, e);
+          }
+        }
+        return Err(e.into());
+      }
+    };
 
     // get file length
     let len = {