add: SVT-AV1 lp (thread cap) config knob

Add encoding.lp (0 = auto) so a long encode can be capped to N logical
processors instead of pinning every core, as a lighter-weight alternative to
the compose cgroup limit. Threaded config -> types.Job -> -svtav1-params via a
testable svtav1Params helper. Settings-UI surfacing stays with #1.

refs #5

cmd/av1dae/main.go

@@ -192,6 +192,7 @@ func processFile(ctx context.Context, inputPath string, cfg *types.Config, enc *
 		MediaType:    mediaType,
 		CRF:          crf,
 		Preset:       preset,
+		LP:           cfg.Encoding.LP,
 		DeleteOrigin: deleteOrigin,
 	}
 

config.example.yaml

@@ -11,6 +11,9 @@ encoding:
   bluray:
     crf: 29
     preset: 3
+  # SVT-AV1 logical-processor (thread) cap so a long encode can't pin every core.
+  # 0 = auto (use all cores). Applies to every profile.
+  lp: 0
 
 paths:
   input: "./input"

internal/encoder/encoder.go

@@ -403,6 +403,17 @@ func (e *Encoder) encodeOpus(ctx context.Context, wavs []string, workDir string)
 	return opusFiles, nil
 }
 
+// svtav1Params builds the -svtav1-params value, appending lp=N (logical
+// processors / encoder thread count) only when lp > 0. lp=0 lets SVT-AV1
+// auto-detect, preserving prior behavior.
+func svtav1Params(lp int) string {
+	p := "film-grain=10:film-grain-denoise=1:scd=1:qm-min=4:qm-max=15:keyint=10s"
+	if lp > 0 {
+		p += fmt.Sprintf(":lp=%d", lp)
+	}
+	return p
+}
+
 func (e *Encoder) encodeVideo(ctx context.Context, input, workDir string, opusFiles []string, job *types.Job, metadata *types.Metadata, interlaced bool, streamLangs []StreamMetadata) error {
 	outFile := filepath.Join(workDir, "output.mkv")
 
@@ -418,7 +429,7 @@ func (e *Encoder) encodeVideo(ctx context.Context, input, workDir string, opusFi
 		}
 	}
 
-	svtParams := fmt.Sprintf("film-grain=10:film-grain-denoise=1:scd=1:qm-min=4:qm-max=15:keyint=10s")
+	svtParams := svtav1Params(job.LP)
 
 	zscaleStr, newWidth, err := e.calculateZscaleWidth(ctx, input, 0)
 	if err != nil {

internal/encoder/encoder_test.go

@@ -0,0 +1,23 @@
+package encoder
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSvtav1Params(t *testing.T) {
+	const base = "film-grain=10:film-grain-denoise=1:scd=1:qm-min=4:qm-max=15:keyint=10s"
+
+	if got := svtav1Params(0); got != base {
+		t.Errorf("lp=0 should not append lp:\n got %q\nwant %q", got, base)
+	}
+	if got := svtav1Params(-1); got != base {
+		t.Errorf("lp<0 should not append lp: got %q", got)
+	}
+	if got := svtav1Params(4); got != base+":lp=4" {
+		t.Errorf("lp=4: got %q, want suffix :lp=4", got)
+	}
+	if got := svtav1Params(4); !strings.HasPrefix(got, base) {
+		t.Errorf("lp set should keep the base params intact: got %q", got)
+	}
+}

pkg/types/types.go

@@ -16,6 +16,7 @@ type Job struct {
 	Metadata     *Metadata
 	CRF          int
 	Preset       int
+	LP           int // SVT-AV1 logical processors; 0 = auto
 	DeleteOrigin bool
 }
 
@@ -46,6 +47,9 @@ type EncodingConfig struct {
 	Bluray EncodingParams `yaml:"bluray"`
 	WebDL  EncodingParams `yaml:"webdl"`
 	TVRip  EncodingParams `yaml:"tvrip"`
+	// LP caps SVT-AV1's logical-processor (thread) count so a long encode can't
+	// pin every core. 0 = let SVT-AV1 auto-detect (default). Applies to all profiles.
+	LP int `yaml:"lp"`
 }
 
 type EncodingParams struct {