make ffmpegopusaudio codec behave according to docs

Author: felix920506

discord/player.py

@@ -355,8 +355,10 @@ class FFmpegOpusAudio(FFmpegAudio):
         The codec to use to encode the audio data.  Normally this would be
         just ``libopus``, but is used by :meth:`FFmpegOpusAudio.from_probe` to
         opportunistically skip pointlessly re-encoding Opus audio data by passing
-        ``copy`` as the codec value.  Any values other than ``copy``, ``opus``, or
-        ``libopus`` will be considered ``libopus``.  Defaults to ``libopus``.
+        ``copy`` as the codec value.  Any values other than ``copy``, or
+        ``libopus`` will be considered ``libopus``. ``opus`` will also be considered
+        ``libopus`` since the ``opus`` encoder is still in development. Defaults to ``libopus``.
+        
 
         .. warning::
 
@@ -407,7 +409,9 @@ def __init__(
         args.append("-i")
         args.append("-" if pipe else source)
 
-        codec = "copy" if codec in ("opus", "libopus") else "libopus"
+        # use "libopus" when "opus" is specified since the "opus" encoder is incomplete
+        # link to ffmpeg docs: https://www.ffmpeg.org/ffmpeg-codecs.html#opus 
+        codec = "copy" if codec == "copy" else "libopus"
 
         args.extend(
             (
@@ -417,17 +421,24 @@ def __init__(
                 "opus",
                 "-c:a",
                 codec,
-                "-ar",
-                "48000",
-                "-ac",
-                "2",
-                "-b:a",
-                f"{bitrate}k",
                 "-loglevel",
                 "warning",
             )
         )
 
+        # only pass in bitrate, sample rate, channels arguments when actually encoding to avoid ffmpeg warnings
+        if codec != "copy":
+            args.extend(
+                (
+                    "-ar",
+                    "48000",
+                    "-ac",
+                    "2",
+                    "-b:a",
+                    f"{bitrate}k",
+                )
+            )
+
         if isinstance(options, str):
             args.extend(shlex.split(options))
 
@@ -501,6 +512,8 @@ def custom_probe(source, executable):
 
         executable = kwargs.get("executable")
         codec, bitrate = await cls.probe(source, method=method, executable=executable)
+        # only re-encode ir source isn't already opus, else directly copy source audio stream
+        codec = "copy" if codec in ("opus", "libopus") else "libopus"
         return cls(source, bitrate=bitrate, codec=codec, **kwargs)  # type: ignore
 
     @classmethod