convert: skip missing album art instead of crashing

beetsplug/convert.py

@@ -532,6 +532,14 @@ def copy_album_art(self, album: Album) -> None:
         if not album or not album.artpath:
             return
 
+        # The stored art path may point to a missing file (e.g. the cover
+        # lives in the album's root directory rather than a per-disc one).
+        if not os.path.isfile(util.syspath(album.artpath)):
+            self._log.info(
+                "Skipping {.art_filepath} (source file not found)", album
+            )
+            return
+
         album_item = album.items().get()
         # Album shouldn't be empty.
         if not album_item:

docs/changelog.rst

@@ -85,6 +85,10 @@ Bug fixes
   the database has been deleted from disk. Missing items are now skipped with a
   warning and the command continues. :bug:`6720`
 - :doc:`plugins/fish`: Fix error on plugin initialization.
+- :doc:`plugins/convert`: ``convert -a`` with ``copy_album_art`` enabled no
+  longer crashes when the stored album art path points to a missing file (for
+  example a multi-disc album whose cover lives in the album root rather than a
+  per-disc directory); the missing art is skipped instead. :bug:`4692`
 
 For plugin developers
 ~~~~~~~~~~~~~~~~~~~~~

test/plugins/test_convert.py

@@ -181,6 +181,21 @@ def test_embed_album_art(self):
         mediafile = MediaFile(self.converted_mp3)
         assert mediafile.images[0].data == image_data
 
+    def test_copy_album_art_missing_source(self, caplog):
+        # A missing/stale art source should be skipped instead of crashing
+        # the conversion (see #4692).
+        self.config["convert"]["copy_album_art"] = True
+        self.album.artpath = os.path.join(_common.RSRC, b"nonexistent.jpg")
+        self.album.store()
+
+        with caplog.at_level("INFO", logger="beets.convert"):
+            self.run_command("convert", "-a", "--yes")
+
+        assert any(
+            "source file not found" in message for message in caplog.messages
+        )
+        assert self.file_endswith(self.converted_mp3, "mp3")
+
     def test_skip_existing(self):
         converted = self.converted_mp3
         self.touch(converted, content="XXX")