Add a niceness option to the FFmpeg class initializer

ffmpeg/asyncio/ffmpeg.py

@@ -19,15 +19,25 @@
 
 
 class FFmpeg(AsyncIOEventEmitter):
-    def __init__(self, executable: str = "ffmpeg"):
-        """Initialize an `FFmpeg` instance using `asyncio`
+    def __init__(self, executable: str = "ffmpeg", niceness: int = 0):
+        """Initialize an `FFmpeg` instance using `asyncio`.
 
         Args:
             executable: The path to the ffmpeg executable. Defaults to "ffmpeg".
+            niceness: The niceness of the ffmpeg process
+            (between -20 and 19, higher niceness is lower priority).
+            Defaults to 0 (no change).
+            On Windows, n < -10 is High priority, -10 <= n < 0 is Above Average,
+            0 < n <= 10 is Below Average, and n > 10 is Idle.
+            On Linux, niceness below 0 requires root privileges.
         """
         super().__init__()
 
         self._executable: str = executable
+        if isinstance(niceness, int) and -20 <= niceness <= 19:
+            self._niceness: int = niceness
+        else:
+            raise ValueError("Niceness must be an int between -20 and 19")
         self._options: Options = Options()
 
         self._process: asyncio.subprocess.Process
@@ -174,11 +184,29 @@ async def execute(
 
         self.emit("start", self.arguments)
 
+        prio_args = {}
+
+        if self._niceness != 0:
+            if is_windows():
+                creationflags = 0
+                if self._niceness < -10:
+                    creationflags = subprocess.HIGH_PRIORITY_CLASS  # type: ignore
+                elif self._niceness < 0:
+                    creationflags = subprocess.ABOVE_NORMAL_PRIORITY_CLASS  # type: ignore
+                elif self._niceness > 10:
+                    creationflags = subprocess.IDLE_PRIORITY_CLASS  # type: ignore
+                elif self._niceness > 0:
+                    creationflags = subprocess.BELOW_NORMAL_PRIORITY_CLASS  # type: ignore
+                prio_args["creationflags"] = creationflags
+            else:
+                prio_args["preexec_fn"] = lambda: os.nice(self._niceness)  # type: ignore
+
         self._process = await create_subprocess(
             *self.arguments,
             stdin=subprocess.PIPE if stream is not None else None,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
+            **prio_args,
         )
 
         self._executed = True

ffmpeg/asyncio/utils.py

@@ -13,7 +13,9 @@ def create_subprocess(*args: Any, **kwargs: Any) -> Awaitable[asyncio.subprocess
     # which is required to gracefully terminate the FFmpeg process.
     # Reference: https://docs.python.org/3/library/asyncio-subprocess.html#asyncio.subprocess.Process.send_signal
     if is_windows():
-        kwargs["creationflags"] = subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore
+        if "creationflags" not in kwargs:
+            kwargs["creationflags"] = 0
+        kwargs["creationflags"] |= subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore
 
     return asyncio.create_subprocess_exec(*args, **kwargs)
 

ffmpeg/ffmpeg.py

@@ -18,15 +18,25 @@
 
 
 class FFmpeg(EventEmitter):
-    def __init__(self, executable: str = "ffmpeg"):
+    def __init__(self, executable: str = "ffmpeg", niceness: int = 0):
         """Initialize an `FFmpeg` instance.
 
         Args:
             executable: The path to the ffmpeg executable. Defaults to "ffmpeg".
+            niceness: The niceness of the ffmpeg process
+            (between -20 and 19, higher niceness is lower priority).
+            Defaults to 0 (no change).
+            On Windows, n < -10 is High priority, -10 <= n < 0 is Above Average,
+            0 < n <= 10 is Below Average, and n > 10 is Idle.
+            On Linux, niceness below 0 requires root privileges.
         """
         super().__init__()
 
         self._executable: str = executable
+        if isinstance(niceness, int) and -20 <= niceness <= 19:
+            self._niceness: int = niceness
+        else:
+            raise ValueError("Niceness must be an int between -20 and 19")
         self._options: Options = Options()
 
         self._process: subprocess.Popen[bytes]
@@ -169,12 +179,30 @@ def execute(self, stream: Optional[Union[bytes, IO[bytes]]] = None, timeout: Opt
 
         self.emit("start", self.arguments)
 
+        prio_args = {}
+
+        if self._niceness != 0:
+            if is_windows():
+                creationflags = 0
+                if self._niceness < -10:
+                    creationflags = subprocess.HIGH_PRIORITY_CLASS  # type: ignore
+                elif self._niceness < 0:
+                    creationflags = subprocess.ABOVE_NORMAL_PRIORITY_CLASS  # type: ignore
+                elif self._niceness > 10:
+                    creationflags = subprocess.IDLE_PRIORITY_CLASS  # type: ignore
+                elif self._niceness > 0:
+                    creationflags = subprocess.BELOW_NORMAL_PRIORITY_CLASS  # type: ignore
+                prio_args["creationflags"] = creationflags
+            else:
+                prio_args["preexec_fn"] = lambda: os.nice(self._niceness)  # type: ignore
+
         self._process = create_subprocess(
             self.arguments,
             bufsize=0,
             stdin=subprocess.PIPE if stream is not None else None,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
+            **prio_args,
         )
 
         with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:

ffmpeg/utils.py

@@ -39,7 +39,9 @@ def create_subprocess(*args: Any, **kwargs: Any) -> subprocess.Popen:
     # which is required to gracefully terminate the FFmpeg process.
     # Reference: https://docs.python.org/3/library/subprocess.html#subprocess.Popen.send_signal
     if is_windows():
-        kwargs["creationflags"] = subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore
+        if "creationflags" not in kwargs:
+            kwargs["creationflags"] = 0
+        kwargs["creationflags"] |= subprocess.CREATE_NEW_PROCESS_GROUP  # type: ignore
 
     return subprocess.Popen(*args, **kwargs)