Rearchitected transcoding to treat codecs and encoders as separate concepts.

core/transcoder/audiocodec.go

@@ -0,0 +1,42 @@
+package transcoder
+
+const audioCodecAAC = "aac"
+
+// aacFFmpegEncoder happens to match audioCodecAAC, but represents the ffmpeg
+// encoder name, which could be "libfdk_aac" or another AAC encoder instead.
+const aacFFmpegEncoder = "aac"
+
+// AudioCodec represents an audio compression format (e.g., AAC, Opus).
+type AudioCodec interface {
+	Name() string
+	DisplayName() string
+	FFmpegEncoderName() string
+}
+
+// AACCodec implements AudioCodec for AAC audio.
+type AACCodec struct{}
+
+func (c *AACCodec) Name() string {
+	return audioCodecAAC
+}
+
+func (c *AACCodec) DisplayName() string {
+	return "AAC"
+}
+
+// FFmpegEncoderName returns the ffmpeg encoder to use. We use the built-in
+// "aac" encoder rather than "libfdk_aac" since it is universally available.
+func (c *AACCodec) FFmpegEncoderName() string {
+	return aacFFmpegEncoder
+}
+
+var audioCodecRegistry = map[string]AudioCodec{
+	audioCodecAAC: &AACCodec{},
+}
+
+func getAudioCodec(name string) AudioCodec {
+	if codec, ok := audioCodecRegistry[name]; ok {
+		return codec
+	}
+	return &AACCodec{}
+}