diff --git a/tauri-app/src-tauri/src/ffmpeg_cmd.rs b/tauri-app/src-tauri/src/ffmpeg_cmd.rs
index 3a2d39c..70b3ab4 100644
--- a/tauri-app/src-tauri/src/ffmpeg_cmd.rs
+++ b/tauri-app/src-tauri/src/ffmpeg_cmd.rs
@@ -737,6 +737,56 @@ pub async fn transcode_for_preview(app: &AppHandle, input_path: &str) -> Result<
         return Err(format!("输入文件不存在: {}", input_path));
     }
 
+    let path_str = input.canonicalize()
+        .unwrap_or(input.to_path_buf())
+        .to_string_lossy()
+        .to_string();
+
+    // 快速检测：如果已经是 H.264 + YUV420p，直接返回原始路径（避免应用自己生成的成品重复转码）
+    let probe_args = vec![
+        "-v".to_string(), "error".to_string(),
+        "-select_streams".to_string(), "v:0".to_string(),
+        "-show_entries".to_string(), "stream=codec_name,pix_fmt,width,height".to_string(),
+        "-of".to_string(), "json".to_string(),
+        path_str.clone(),
+    ];
+
+    let probe_result = app.shell().sidecar("ffprobe")
+        .and_then(|s| s.args(probe_args).spawn());
+    if let Ok((mut rx, child)) = probe_result {
+        let mut stdout = String::new();
+        let probe_future = async {
+            while let Some(event) = rx.recv().await {
+                match event {
+                    CommandEvent::Stdout(line) => stdout.push_str(&String::from_utf8_lossy(&line)),
+                    CommandEvent::Terminated(status) if status.code == Some(0) => return Ok(()),
+                    _ => {}
+                }
+            }
+            Ok::<(), ()>(())
+        };
+        match tokio::time::timeout(std::time::Duration::from_secs(3), probe_future).await {
+            Ok(Ok(())) => {
+                if let Ok(parsed) = serde_json::from_str::<serde_json::Value>(&stdout) {
+                    if let Some(stream) = parsed.get("streams").and_then(|s| s.as_array()).and_then(|a| a.first()) {
+                        let codec = stream.get("codec_name").and_then(|v| v.as_str()).unwrap_or("");
+                        let pix_fmt = stream.get("pix_fmt").and_then(|v| v.as_str()).unwrap_or("");
+                        // 应用生成的视频通常是 1080p 及以下；若用户上传了 4K H.264，仍转码为 540p 代理以保证预览流畅
+                        let width = stream.get("width").and_then(|v| v.as_u64()).unwrap_or(0);
+                        let height = stream.get("height").and_then(|v| v.as_u64()).unwrap_or(0);
+                        if codec == "h264" && pix_fmt == "yuv420p" && width <= 1920 && height <= 1920 {
+                            return Ok(path_str);
+                        }
+                    }
+                }
+            }
+            _ => {
+                // 超时或异常：强制结束 ffprobe，避免僵尸进程
+                let _ = child.kill();
+            }
+        }
+    }
+
     // 获取文件元数据用于缓存 key
     let metadata = std::fs::metadata(input_path)
         .map_err(|e| format!("无法读取文件元数据: {}", e))?;
@@ -749,10 +799,6 @@ pub async fn transcode_for_preview(app: &AppHandle, input_path: &str) -> Result<
     let file_size = metadata.len();
 
     // 计算缓存路径（基于文件路径 hash + 大小 + 修改时间）
-    let path_str = input.canonicalize()
-        .unwrap_or(input.to_path_buf())
-        .to_string_lossy()
-        .to_string();
     let path_hash = {
         use std::collections::hash_map::DefaultHasher;
         use std::hash::{Hash, Hasher};