diff --git a/copyparty/mtag.py b/copyparty/mtag.py
index e006b688..b9058a5a 100644
--- a/copyparty/mtag.py
+++ b/copyparty/mtag.py
@@ -200,9 +200,10 @@ def au_unpk(
 
     except Exception as ex:
         if ret:
-            t = "failed to decompress audio file %r: %r"
+            t = "failed to decompress file %r: %r"
             log(t % (abspath, ex))
             wunlink(log, ret, vn.flags if vn else VF_CAREFUL)
+            return ""
 
         return abspath
 
@@ -422,10 +423,17 @@ def get_cover_from_epub(log: "NamedLogger", abspath: str) -> Optional[IO[bytes]]
             # This might be an EPUB2 file, try the legacy way of specifying covers
             coverimage_path = _get_cover_from_epub2(log, package_root, package_ns)
 
+        if not coverimage_path:
+            raise Exception("no cover inside epub")
+
         # This url is either absolute (in the .epub) or relative to the package document
         adjusted_cover_path = urljoin(rootfile_path, coverimage_path)
 
-        return z.open(adjusted_cover_path)
+        try:
+            return z.open(adjusted_cover_path)
+        except KeyError:
+            t = "epub: cover specified in package document, but doesn't exist: %s"
+            log(t % (adjusted_cover_path,))
 
 
 def _get_cover_from_epub2(
@@ -643,6 +651,9 @@ class MTag(object):
             return self._get(abspath)
 
         ap = au_unpk(self.log, self.args.au_unpk, abspath)
+        if not ap:
+            return {}
+
         ret = self._get(ap)
         if ap != abspath:
             wunlink(self.log, ap, VF_CAREFUL)
@@ -748,6 +759,9 @@ class MTag(object):
             ap = abspath
 
         ret: dict[str, Any] = {}
+        if not ap:
+            return ret
+
         for tagname, parser in sorted(parsers.items(), key=lambda x: (x[1].pri, x[0])):
             try:
                 cmd = [parser.bin, ap]
diff --git a/copyparty/th_srv.py b/copyparty/th_srv.py
index 86c3c469..2faee236 100644
--- a/copyparty/th_srv.py
+++ b/copyparty/th_srv.py
@@ -381,7 +381,7 @@ class ThumbSrv(object):
             else:
                 ap_unpk = abspath
 
-            if not bos.path.exists(tpath):
+            if ap_unpk and not bos.path.exists(tpath):
                 tex = tpath.rsplit(".", 1)[-1]
                 want_mp3 = tex == "mp3"
                 want_opus = tex in ("opus", "owa", "caf")
@@ -424,12 +424,14 @@ class ThumbSrv(object):
             except:
                 pass
 
+            conv_ok = False
             for fun in funs:
                 try:
                     if not png_ok and tpath.endswith(".png"):
                         raise Exception("png only allowed for waveforms")
 
                     fun(ap_unpk, ttpath, fmt, vn)
+                    conv_ok = True
                     break
                 except Exception as ex:
                     msg = "%s could not create thumbnail of %r\n%s"
@@ -451,16 +453,20 @@ class ThumbSrv(object):
                         except:
                             pass
 
-            if abspath != ap_unpk:
+            if abspath != ap_unpk and ap_unpk:
                 wunlink(self.log, ap_unpk, vn.flags)
 
             try:
                 atomic_move(self.log, ttpath, tpath, vn.flags)
             except Exception as ex:
-                if not os.path.exists(tpath):
+                if conv_ok and not os.path.exists(tpath):
                     t = "failed to move  [%s]  to  [%s]:  %r"
                     self.log(t % (ttpath, tpath, ex), 3)
-                pass
+                elif not conv_ok:
+                    try:
+                        open(tpath, "ab").close()
+                    except:
+                        pass
 
             untemp = []
             with self.mutex:
@@ -682,7 +688,7 @@ class ThumbSrv(object):
             return
 
         c: Union[str, int] = "90"
-        t = "FFmpeg failed (probably a corrupt video file):\n"
+        t = "FFmpeg failed (probably a corrupt file):\n"
         if (
             (not self.args.th_ff_jpg or time.time() - int(self.args.th_ff_jpg) < 60)
             and cmd[-1].lower().endswith(b".webp")