Let Emby select audio stream

Author: tces1

README.md

@@ -11,7 +11,7 @@ It is intentionally narrow: normal API traffic is forwarded to the upstream serv
 - Client profile matching by `User-Agent` and `X-Emby-Authorization`.
 - PlaybackInfo rewriting for matched profiles.
 - Local FFmpeg HLS sessions under `/streambridge/transcode/`.
-- Audio track selection through Emby `AudioStreamIndex`, mapped to the matching FFmpeg audio stream.
+- Audio track selection through Emby `AudioStreamIndex`, with local transcode restart on audio changes.
 - Playback lifecycle tracking through Emby `/Sessions/Playing*` check-ins plus HLS access.
 - Conservative output target: H.264 video, AAC audio, HLS MPEG-TS segments.
 

internal/proxy/server.go

@@ -242,9 +242,7 @@ func (s *Server) upstreamURL(in *url.URL) string {
 func transcodeInputURL(upstream *url.URL, id string, r *http.Request) string {
 	u := *upstream
 	u.Path = singleJoiningSlash(upstream.Path, path.Join("/emby/Videos", id, "stream"))
-	query := r.URL.Query()
-	query.Del("AudioStreamIndex")
-	u.RawQuery = query.Encode()
+	u.RawQuery = r.URL.RawQuery
 	return u.String()
 }
 

internal/proxy/transcode_input_test.go

@@ -27,7 +27,7 @@ func TestTranscodeInputURLPreservesStartTimeTicks(t *testing.T) {
 	}
 }
 
-func TestTranscodeInputURLStripsAudioStreamIndexForLocalMapping(t *testing.T) {
+func TestTranscodeInputURLPreservesAudioStreamIndexForEmbySelection(t *testing.T) {
 	upstream, err := url.Parse("http://upstream.local")
 	if err != nil {
 		t.Fatal(err)
@@ -36,8 +36,8 @@ func TestTranscodeInputURLStripsAudioStreamIndexForLocalMapping(t *testing.T) {
 
 	got := transcodeInputURL(upstream, "item123", req)
 
-	if strings.Contains(got, "AudioStreamIndex=") {
-		t.Fatalf("input url should not forward AudioStreamIndex to upstream when local ffmpeg maps audio: %s", got)
+	if !strings.Contains(got, "AudioStreamIndex=2") {
+		t.Fatalf("input url should forward AudioStreamIndex so Emby returns the selected audio track: %s", got)
 	}
 	if !strings.Contains(got, "MediaSourceId=source1") || !strings.Contains(got, "X-Emby-Token=abc") {
 		t.Fatalf("input url should preserve non-audio query params: %s", got)

internal/transcode/ffmpeg_args_test.go

@@ -103,7 +103,7 @@ func TestBuildFFmpegArgsAppliesVAAPIHardwareDecodeBeforeInput(t *testing.T) {
 	}
 }
 
-func TestBuildFFmpegArgsMapsRequestedEmbyAudioStreamIndex(t *testing.T) {
+func TestBuildFFmpegArgsMapsFirstAudioStreamReturnedByEmby(t *testing.T) {
 	session := &Session{
 		ID:  "item123",
 		Dir: t.TempDir(),
@@ -125,7 +125,7 @@ func TestBuildFFmpegArgsMapsRequestedEmbyAudioStreamIndex(t *testing.T) {
 	if len(mapIndexes) < 2 {
 		t.Fatalf("missing map args: %v", args)
 	}
-	if got := args[mapIndexes[1]+1]; got != "0:a:1?" {
+	if got := args[mapIndexes[1]+1]; got != "0:a:0?" {
 		t.Fatalf("audio map = %q, args=%v", got, args)
 	}
 }

internal/transcode/manager.go

@@ -904,24 +904,7 @@ func buildFFmpegArgs(session *Session, request Request, options ...FFmpegOptions
 }
 
 func audioMapArg(session *Session, request Request) string {
-	ordinal := audioOrdinalForRequest(session, request)
-	return fmt.Sprintf("0:a:%d?", ordinal)
-}
-
-func audioOrdinalForRequest(session *Session, request Request) int {
-	if request.AudioStreamIndex < 0 {
-		return 0
-	}
-	media := request.Media
-	if media.IsZero() && session != nil {
-		media = session.Media
-	}
-	for _, stream := range media.AudioStreams {
-		if stream.Index == request.AudioStreamIndex && stream.Ordinal >= 0 {
-			return stream.Ordinal
-		}
-	}
-	return 0
+	return "0:a:0?"
 }
 
 func appendHardwareDecodeArgs(args []string, options FFmpegOptions) []string {