delete x264_2pass.log and x264_2pass.log.mbtree files after encoding

src/encode.moon

@@ -441,5 +441,7 @@ encode = (region, startTime, endTime) ->
 
 		-- Clean up pass log file.
 		os.remove(get_pass_logfile_path(out_path))
+		os.remove "x264_2pass.log"
+		os.remove "x264_2pass.log.mbtree"
 		if is_temporary
 			os.remove(path)

tests/testcases/test_x264_pass_log_cleanup.py

@@ -0,0 +1,28 @@
+from .base_test_case import BaseTestCase
+
+
+class TestX264PassLogCleanup(BaseTestCase):
+    def test_bitrate_twopass_removes_x264_stats(self):
+        self.openTestVideoFile(self.createVideo(size="64x64"))
+        # Keep the output directory distinct from mpv's working directory:
+        # libx264 writes its stats files into the encoder's current directory,
+        # which is what the bug left behind.
+        output_dir = self.tempdir / "out"
+        output_dir.mkdir()
+        self.encodeClip(0, 1, options={
+            "output_format": "avc", "target_filesize": 250,
+            "twopass": True, "threads": 2, "crf": 20,
+            "output_template": "x264-twopass",
+            "output_directory": str(output_dir),
+        })
+        output = output_dir / "x264-twopass.mp4"
+        self.assertGreater(output.stat().st_size, 0)
+        self.assertGreater(len(self.decodeVideo(output)), 0)
+        # The stats files only exist because a real second pass looked them up;
+        # make sure the regression test cannot pass vacuously.
+        self.waitUntil(lambda: "--ovcopts-add=flags=+pass2" in self.getLog(),
+                       "second pass command")
+        self.assertIn("First-pass command line:", self.getLog())
+        for name in ("x264_2pass.log", "x264_2pass.log.mbtree"):
+            self.assertFalse((self.tempdir / name).exists(),
+                             f"{name} was left behind after encoding")