Move media::AudioCodec to its own source file

media/base/audio_codecs.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/base/audio_codecs.h"
+
+#include "base/logging.h"
+
+namespace media {
+
+// These names come from src/third_party/ffmpeg/libavcodec/codec_desc.c
+std::string GetCodecName(AudioCodec codec) {
+  switch (codec) {
+    case kUnknownAudioCodec:
+      return "unknown";
+    case kCodecAAC:
+      return "aac";
+    case kCodecMP3:
+      return "mp3";
+    case kCodecPCM:
+    case kCodecPCM_S16BE:
+    case kCodecPCM_S24BE:
+      return "pcm";
+    case kCodecVorbis:
+      return "vorbis";
+    case kCodecFLAC:
+      return "flac";
+    case kCodecAMR_NB:
+      return "amr_nb";
+    case kCodecAMR_WB:
+      return "amr_wb";
+    case kCodecPCM_MULAW:
+      return "pcm_mulaw";
+    case kCodecGSM_MS:
+      return "gsm_ms";
+    case kCodecOpus:
+      return "opus";
+    case kCodecPCM_ALAW:
+      return "pcm_alaw";
+    case kCodecEAC3:
+      return "eac3";
+    case kCodecALAC:
+      return "alac";
+    case kCodecAC3:
+      return "ac3";
+  }
+  NOTREACHED();
+  return "";
+}
+
+}  // namespace media