Cap transcode output at 1080p

Author: tces1

README.md

@@ -14,6 +14,7 @@ It is intentionally narrow: normal API traffic is forwarded to the upstream serv
 - 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.
+- Video output is capped at 1920x1080 and keeps aspect ratio.
 
 Not included: virtual libraries, RSS, cover generation, scraping, database storage, or a management UI.
 

docker/README.md

@@ -26,6 +26,7 @@ Edit `config/config.json` before startup, or copy it to `config/config.local.jso
 - set `transcode.hardware_decode` to `vaapi` to use Intel or AMD VAAPI hardware decode through `/dev/dri`
 - startup probes VAAPI support, including device initialization, and falls back to software decode when the device, driver, or ffmpeg support is unavailable
 - the image includes common Intel and AMD VAAPI userspace drivers plus `vainfo`
+- video output is capped at 1920x1080 while preserving aspect ratio
 
 For GitHub Actions publishing to Docker Hub, set `DOCKERHUB_USERNAME` and `DOCKERHUB_TOKEN` in the repository secrets.
 

internal/transcode/ffmpeg_args_test.go

@@ -106,6 +106,27 @@ func TestBuildFFmpegArgsAppliesVAAPIHardwareDecodeBeforeInput(t *testing.T) {
 	}
 }
 
+func TestBuildFFmpegArgsCapsVideoOutputTo1080p(t *testing.T) {
+	session := &Session{
+		ID:  "item123",
+		Dir: t.TempDir(),
+	}
+
+	args := buildFFmpegArgs(session, Request{InputURL: "http://upstream/stream"})
+
+	vfIndex := slices.Index(args, "-vf")
+	if vfIndex < 0 {
+		t.Fatalf("missing video scale filter: %v", args)
+	}
+	got := args[vfIndex+1]
+	if !strings.Contains(got, "scale=") {
+		t.Fatalf("expected scale filter, got %q", got)
+	}
+	if !strings.Contains(got, "1920") || !strings.Contains(got, "1080") {
+		t.Fatalf("expected 1080p cap in scale filter, got %q", got)
+	}
+}
+
 func TestBuildFFmpegArgsMapsFirstAudioStreamReturnedByEmby(t *testing.T) {
 	session := &Session{
 		ID:  "item123",

internal/transcode/manager.go

@@ -23,6 +23,8 @@ import (
 var ErrTooManySessions = errors.New("too many transcode sessions")
 
 const defaultRestartGraceTimeout = 500 * time.Millisecond
+const maxTranscodeWidth = 1920
+const maxTranscodeHeight = 1080
 
 type Options struct {
 	MaxSessions           int
@@ -933,6 +935,7 @@ func buildFFmpegArgs(session *Session, request Request, options ...FFmpegOptions
 		"-i", request.InputURL,
 		"-map", "0:v:0",
 		"-map", audioMapArg(session, request),
+		"-vf", fmt.Sprintf("scale=w=%d:h=%d:force_original_aspect_ratio=decrease:force_divisible_by=2", maxTranscodeWidth, maxTranscodeHeight),
 		"-c:v", "libx264",
 		"-preset", "veryfast",
 		"-profile:v", "high",