diff --git a/copyparty/mtag.py b/copyparty/mtag.py
index 82ff63b6..d9971343 100644
--- a/copyparty/mtag.py
+++ b/copyparty/mtag.py
@@ -118,7 +118,7 @@ def ffprobe(
         b"--",
         fsenc(abspath),
     ]
-    rc, so, se = runcmd(cmd, timeout=timeout)
+    rc, so, se = runcmd(cmd, timeout=timeout, nice=True)
     retchk(rc, cmd, se)
     return parse_ffprobe(so)
 
@@ -562,6 +562,7 @@ class MTag(object):
 
                 args = {
                     "env": env,
+                    "nice": True,
                     "timeout": parser.timeout,
                     "kill": parser.kill,
                     "capture": parser.capture,
@@ -572,11 +573,6 @@ class MTag(object):
                     zd.update(ret)
                     args["sin"] = json.dumps(zd).encode("utf-8", "replace")
 
-                if WINDOWS:
-                    args["creationflags"] = 0x4000
-                else:
-                    cmd = ["nice"] + cmd
-
                 bcmd = [sfsenc(x) for x in cmd[:-1]] + [fsenc(cmd[-1])]
                 rc, v, err = runcmd(bcmd, **args)  # type: ignore
                 retchk(rc, bcmd, err, self.log, 5, self.args.mtag_v)
diff --git a/copyparty/th_srv.py b/copyparty/th_srv.py
index e4398887..233de259 100644
--- a/copyparty/th_srv.py
+++ b/copyparty/th_srv.py
@@ -468,7 +468,7 @@ class ThumbSrv(object):
 
     def _run_ff(self, cmd: list[bytes], vn: VFS) -> None:
         # self.log((b" ".join(cmd)).decode("utf-8"))
-        ret, _, serr = runcmd(cmd, timeout=vn.flags["convt"])
+        ret, _, serr = runcmd(cmd, timeout=vn.flags["convt"], nice=True)
         if not ret:
             return
 
diff --git a/copyparty/util.py b/copyparty/util.py
index 297972a2..95388714 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -2508,9 +2508,34 @@ def killtree(root: int) -> None:
             pass
 
 
+def _find_nice() -> str:
+    if WINDOWS:
+        return ""  # use creationflags
+    
+    try:
+        zs = shutil.which("nice")
+        if zs:
+            return zs
+    except:
+        pass
+
+    # busted PATHs and/or py2
+    for zs in ("/bin", "/sbin", "/usr/bin", "/usr/sbin"):
+        zs += "/nice"
+        if os.path.exists(zs):
+            return zs
+
+    return ""
+
+
+NICES = _find_nice()
+NICEB = NICES.encode("utf-8")
+
+
 def runcmd(
     argv: Union[list[bytes], list[str]], timeout: Optional[float] = None, **ka: Any
 ) -> tuple[int, str, str]:
+    isbytes = isinstance(argv[0], (bytes, bytearray))
     kill = ka.pop("kill", "t")  # [t]ree [m]ain [n]one
     capture = ka.pop("capture", 3)  # 0=none 1=stdout 2=stderr 3=both
 
@@ -2524,13 +2549,22 @@ def runcmd(
     berr: bytes
 
     if ANYWIN:
-        if isinstance(argv[0], (bytes, bytearray)):
+        if isbytes:
             if argv[0] in CMD_EXEB:
                 argv[0] += b".exe"
         else:
             if argv[0] in CMD_EXES:
                 argv[0] += ".exe"
 
+    if ka.pop("nice", None):
+        if WINDOWS:
+            ka["creationflags"] = 0x4000
+        elif NICEB:
+            if isbytes:
+                argv = [NICEB] + argv
+            else:
+                argv = [NICES] + argv
+
     p = sp.Popen(argv, stdout=cout, stderr=cerr, **ka)
     if not timeout or PY2:
         bout, berr = p.communicate(sin)
@@ -2678,6 +2712,7 @@ def _parsehook(
 
     sp_ka = {
         "env": env,
+        "nice": True,
         "timeout": tout,
         "kill": kill,
         "capture": cap,