fix: use ADTS for AAC transcoding, temporarily exclude AAC from transcode decisions (#5167)

* fix: use ADTS format for AAC transcoding to avoid silent output on ffmpeg 8.0+

The fragmented MP4 muxer (`-f ipod -movflags frag_keyframe+empty_moov`)
produces corrupt/silent audio when ffmpeg pipes to stdout, confirmed on
ffmpeg 8.0+. The moof atom offset values are zeroed out in pipe mode,
causing AAC decoder errors. Switch to `-f adts` (raw AAC framing) which
works reliably via pipe and is widely supported by clients including
UPnP/Sonos devices.

* fix: exclude AAC from transcode decision, as it is not working for Sonos.

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

core/stream/aliases_test.go

@@ -0,0 +1,30 @@
+package stream
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Aliases", func() {
+	Describe("IsAACCodec", func() {
+		It("returns true for AAC and its aliases", func() {
+			Expect(IsAACCodec("aac")).To(BeTrue())
+			Expect(IsAACCodec("AAC")).To(BeTrue())
+			Expect(IsAACCodec("adts")).To(BeTrue())
+			Expect(IsAACCodec("m4a")).To(BeTrue())
+			Expect(IsAACCodec("mp4")).To(BeTrue())
+			Expect(IsAACCodec("m4b")).To(BeTrue())
+		})
+
+		It("returns false for non-AAC formats", func() {
+			Expect(IsAACCodec("mp3")).To(BeFalse())
+			Expect(IsAACCodec("opus")).To(BeFalse())
+			Expect(IsAACCodec("flac")).To(BeFalse())
+			Expect(IsAACCodec("ogg")).To(BeFalse())
+		})
+
+		It("returns false for empty string", func() {
+			Expect(IsAACCodec("")).To(BeFalse())
+		})
+	})
+})