feat: Ogg Vorbis / Ogg Opus / FLAC decode, capture SOURCE Ogg headers

Transcoder and AutoDJ now handle any of MP3, Ogg Vorbis, Ogg Opus or
native FLAC as input instead of only MP3. A new OpenDecoder factory
sniffs the first bytes (ID3/MP3 sync, OggS with OpusHead/vorbis, fLaC)
and returns a PCMDecoder producing interleaved S16LE stereo PCM. This
replaces the direct mp3.NewDecoder calls in relay/transcode.go and
relay/streamer.go. Output encoding still targets MP3 (shine) or Opus
(kazzmir opus-go) — AAC is intentionally not included because no
pure-Go encoder is viable.

validateAudioFile now accepts OggS and fLaC magic bytes so AutoDJ will
play .ogg/.opus/.flac files from disk.

Fix BOS/Tags handling on the Icecast SOURCE handler: the code captures
the initial Ogg pages (those with granule_position == 0 or the
continuation sentinel) as bytes flow in, then stores them on the
Stream as OggHead / OggHeaderOffset. Late-joining listeners get the
full codec setup prepended instead of "Codec not found". Triggered by
Content-Type of application/ogg or audio/ogg (plus variants).

New deps: github.com/jfreymuth/oggvorbis, github.com/mewkiz/flac. Both
pure Go, no CGO required.

Added relay/decode_test.go covering the Ogg page walker and the
decoder sniff.

Author: DatanoiseTV

go.mod

@@ -34,9 +34,15 @@ require (
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/go-multierror v1.1.0 // indirect
+	github.com/icza/bitio v1.1.0 // indirect
+	github.com/jfreymuth/oggvorbis v1.0.5 // indirect
+	github.com/jfreymuth/vorbis v1.0.2 // indirect
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/mewkiz/flac v1.0.13 // indirect
+	github.com/mewkiz/pkg v0.0.0-20250417130911-3f050ff8c56d // indirect
+	github.com/mewpkg/term v0.0.0-20241026122259-37a80af23985 // indirect
 	github.com/mitchellh/mapstructure v1.4.1 // indirect
 	github.com/pion/datachannel v1.6.0 // indirect
 	github.com/pion/dtls/v3 v3.1.2 // indirect

go.sum

@@ -49,6 +49,13 @@ github.com/hashicorp/errwrap v1.1.0 h1:OxrOeh75EUXMY8TBjag2fzXGZ40LB6IKw45YeGUDY
 github.com/hashicorp/errwrap v1.1.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-multierror v1.1.0 h1:B9UzwGQJehnUY1yNrnwREHc3fGbC2xefo8g4TbElacI=
 github.com/hashicorp/go-multierror v1.1.0/go.mod h1:spPvp8C1qA32ftKqdAHm4hHTbPw+vmowP0z+KUhOZdA=
+github.com/icza/bitio v1.1.0 h1:ysX4vtldjdi3Ygai5m1cWy4oLkhWTAi+SyO6HC8L9T0=
+github.com/icza/bitio v1.1.0/go.mod h1:0jGnlLAx8MKMr9VGnn/4YrvZiprkvBelsVIbA9Jjr9A=
+github.com/icza/mighty v0.0.0-20180919140131-cfd07d671de6/go.mod h1:xQig96I1VNBDIWGCdTt54nHt6EeI639SmHycLYL7FkA=
+github.com/jfreymuth/oggvorbis v1.0.5 h1:u+Ck+R0eLSRhgq8WTmffYnrVtSztJcYrl588DM4e3kQ=
+github.com/jfreymuth/oggvorbis v1.0.5/go.mod h1:1U4pqWmghcoVsCJJ4fRBKv9peUJMBHixthRlBeD6uII=
+github.com/jfreymuth/vorbis v1.0.2 h1:m1xH6+ZI4thH927pgKD8JOH4eaGRm18rEE9/0WKjvNE=
+github.com/jfreymuth/vorbis v1.0.2/go.mod h1:DoftRo4AznKnShRl1GxiTFCseHr4zR9BN3TWXyuzrqQ=
 github.com/jinzhu/inflection v1.0.0 h1:K317FqzuhWc8YvSVlFMCCUb36O/S9MCKRDI7QkRKD/E=
 github.com/jinzhu/inflection v1.0.0/go.mod h1:h+uFLlag+Qp1Va5pdKtLDYj+kHp5pxUVkryuEj+Srlc=
 github.com/jinzhu/now v1.1.5 h1:/o9tlHleP7gOFmsnYNz3RGnqzefHA47wQpKrrdTIwXQ=
@@ -57,6 +64,12 @@ github.com/kazzmir/opus-go v1.2.1 h1:uKHJgA4zlZv60eatfwGBhLdrovlPdRVBVco22MQQvmU
 github.com/kazzmir/opus-go v1.2.1/go.mod h1:oKDlLYxYVpknE4zKDmJyiLPB9RyhKw0n/l7EoPr6000=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/mewkiz/flac v1.0.13 h1:6wF8rRQKBFW159Daqx6Ro7K5ZnlVhHUKfS5aTsC4oXs=
+github.com/mewkiz/flac v1.0.13/go.mod h1:HfPYDA+oxjyuqMu2V+cyKcxF51KM6incpw5eZXmfA6k=
+github.com/mewkiz/pkg v0.0.0-20250417130911-3f050ff8c56d h1:IL2tii4jXLdhCeQN69HNzYYW1kl0meSG0wt5+sLwszU=
+github.com/mewkiz/pkg v0.0.0-20250417130911-3f050ff8c56d/go.mod h1:SIpumAnUWSy0q9RzKD3pyH3g1t5vdawUAPcW5tQrUtI=
+github.com/mewpkg/term v0.0.0-20241026122259-37a80af23985 h1:h8O1byDZ1uk6RUXMhj1QJU3VXFKXHDZxr4TXRPGeBa8=
+github.com/mewpkg/term v0.0.0-20241026122259-37a80af23985/go.mod h1:uiPmbdUbdt1NkGApKl7htQjZ8S7XaGUAVulJUJ9v6q4=
 github.com/mitchellh/mapstructure v1.4.1 h1:CpVNEelQCZBooIPDn+AR3NpivK/TIKU8bDxdASFVQag=
 github.com/mitchellh/mapstructure v1.4.1/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/pion/datachannel v1.6.0 h1:XecBlj+cvsxhAMZWFfFcPyUaDZtd7IJvrXqlXD/53i0=