fix: add video duration safety buffer

Author: Sushanth012

app/services/video.py

@@ -314,15 +314,19 @@ def _format_ffmpeg_concat_path(file_path: str) -> str:
 
 
 def concat_video_clips_with_ffmpeg(
-    clip_files: List[str], output_file: str, threads: int, output_dir: str
+    clip_files: List[str],
+    output_file: str,
+    threads: int,
+    output_dir: str,
+    max_duration: float | None = None,
 ):
     concat_list_file = os.path.join(output_dir, "ffmpeg-concat-list.txt")
     with open(concat_list_file, "w", encoding="utf-8") as fp:
         for clip_file in clip_files:
             fp.write(f"file '{_format_ffmpeg_concat_path(clip_file)}'\n")
 
     def build_command(codec: str) -> list[str]:
-        return [
+        command = [
             utils.get_ffmpeg_binary(),
             "-y",
             "-f",
@@ -337,8 +341,11 @@ def build_command(codec: str) -> list[str]:
             str(threads or 2),
             "-pix_fmt",
             "yuv420p",
-            output_file,
         ]
+        if max_duration is not None and max_duration > 0:
+            command.extend(["-t", f"{max_duration:.3f}"])
+        command.append(output_file)
+        return command
 
     def run_concat(codec: str):
         command = build_command(codec)
@@ -719,21 +726,14 @@ def combine_videos(
         logger.warning("no clips available for merging")
         return combined_video_path
 
-    # if there is only one clip, use it directly
-    if len(processed_clips) == 1:
-        logger.info("using single clip directly")
-        shutil.copy(processed_clips[0].file_path, combined_video_path)
-        delete_files([processed_clips[0].file_path])
-        logger.info("video combining completed")
-        return combined_video_path
-
     clip_files = [clip.file_path for clip in processed_clips]
     logger.info(f"concatenating {len(clip_files)} clips with ffmpeg")
     concat_video_clips_with_ffmpeg(
         clip_files=clip_files,
         output_file=combined_video_path,
         threads=threads,
         output_dir=output_dir,
+        max_duration=audio_duration,
     )
 
     # clean temp files

test/services/test_video.py

@@ -485,7 +485,7 @@ def _open_fake_video_clip(video_path):
                     with patch.object(
                         vd, "_write_videofile_with_codec_fallback"
                     ) as write_mock:
-                        with patch.object(vd, "concat_video_clips_with_ffmpeg"):
+                        with patch.object(vd, "concat_video_clips_with_ffmpeg") as concat_mock:
                             with patch.object(vd, "delete_files"):
                                 result = vd.combine_videos(
                                     combined_video_path=combined_video_path,
@@ -499,6 +499,31 @@ def _open_fake_video_clip(video_path):
 
         self.assertEqual(result, combined_video_path)
         self.assertEqual(write_mock.call_count, 4)
+        self.assertEqual(concat_mock.call_args.kwargs["max_duration"], 10.0)
+
+    def test_concat_video_clips_limits_output_to_audio_duration(self):
+        """最终拼接时应裁到音频时长，避免安全余量带来明显静音尾巴。"""
+
+        def fake_run(command, capture_output, text, check):
+            return types.SimpleNamespace(returncode=0, stdout="", stderr="")
+
+        with tempfile.TemporaryDirectory() as temp_dir:
+            clip_file = os.path.join(temp_dir, "clip.mp4")
+            output_file = os.path.join(temp_dir, "combined.mp4")
+            Path(clip_file).write_bytes(b"fake")
+
+            with patch.object(vd.subprocess, "run", side_effect=fake_run) as run:
+                vd.concat_video_clips_with_ffmpeg(
+                    clip_files=[clip_file],
+                    output_file=output_file,
+                    threads=1,
+                    output_dir=temp_dir,
+                    max_duration=10.0,
+                )
+
+        command = run.call_args.args[0]
+        self.assertEqual(command[command.index("-t") + 1], "10.000")
+        self.assertLess(command.index("-t"), command.index(output_file))
 
     def test_prioritize_unique_source_clips_uses_each_source_before_reuse(self):
         """