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/ffmpeg/ffmpeg.go

@@ -283,7 +283,7 @@ var formatCodecMap = map[string]string{
 var formatOutputMap = map[string]string{
 	"mp3":  "mp3",
 	"opus": "opus",
-	"aac":  "ipod",
+	"aac":  "adts",
 	"flac": "flac",
 }
 
@@ -339,11 +339,6 @@ func buildDynamicArgs(opts TranscodeOptions) []string {
 		args = append(args, "-f", outputFmt)
 	}
 
-	// For AAC in MP4 container, enable fragmented MP4 for pipe-safe streaming
-	if opts.Format == "aac" {
-		args = append(args, "-movflags", "frag_keyframe+empty_moov")
-	}
-
 	args = append(args, "-")
 	return args
 }