fix: honor Set Framerate on overlay input streams

ffmpeg.go

@@ -11,6 +11,7 @@ import (
 type FilterComplexBuilder struct {
 	filterComplex *strings.Builder
 	style         *StyleOptions
+	framerate     int
 	termWidth     int
 	termHeight    int
 	prevStageName string
@@ -50,6 +51,7 @@ func NewVideoFilterBuilder(videoOpts *VideoOptions) *FilterComplexBuilder {
 		termHeight:    termHeight,
 		termWidth:     termWidth,
 		style:         videoOpts.Style,
+		framerate:     videoOpts.Framerate,
 		prevStageName: "padded",
 	}
 }
@@ -104,17 +106,30 @@ func calcTermDimensions(style StyleOptions) (int, int) {
 	return width, height
 }
 
+// fps pins a secondary stream to the target framerate. The window bar and
+// margin fill sources (lavfi color, looped images) all default to 25fps, and
+// they are the *main* input of the overlays below, so without this the whole
+// render is forced to 25fps regardless of `Set Framerate`.
+// Returns an empty string for screenshots, which have no framerate.
+func (fb *FilterComplexBuilder) fps() string {
+	if fb.framerate <= 0 {
+		return ""
+	}
+	return fmt.Sprintf(",fps=%d", fb.framerate)
+}
+
 // WithWindowBar adds window bar options to ffmepg filter_complex.
 func (fb *FilterComplexBuilder) WithWindowBar(barStream int) *FilterComplexBuilder {
 	if fb.style.WindowBar != "" {
 		fb.filterComplex.WriteString(";")
 		_, _ = fmt.Fprintf(
 			fb.filterComplex,
 			`
-			[%d]loop=-1[loopbar];
+			[%d]loop=-1%s[loopbar];
 			[loopbar][%s]overlay=0:%d[withbar]
 			`,
 			barStream,
+			fb.fps(),
 			fb.prevStageName,
 			fb.style.WindowBarSize,
 		)
@@ -154,12 +169,13 @@ func (fb *FilterComplexBuilder) WithMarginFill(marginStream int) *FilterComplexB
 		_, _ = fmt.Fprintf(
 			fb.filterComplex,
 			`
-			[%d]scale=%d:%d[bg];
+			[%d]scale=%d:%d%s[bg];
 			[bg][%s]overlay=(W-w)/2:(H-h)/2:shortest=1[withbg]
 			`,
 			marginStream,
 			fb.style.Width,
 			fb.style.Height,
+			fb.fps(),
 			fb.prevStageName,
 		)
 		fb.prevStageName = "withbg"

ffmpeg_test.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+// The margin fill and window bar sources default to 25fps and are the *main*
+// input of their overlay, so they must be pinned to the target framerate or
+// they silently override `Set Framerate`.
+func TestSecondaryStreamsUseFramerate(t *testing.T) {
+	opts := DefaultVideoOptions()
+	opts.Framerate = 60
+	opts.Style = DefaultStyleOptions()
+	opts.Style.WindowBar = "Colorful"
+	opts.Style.MarginFill = "#000000"
+
+	got := strings.Join(NewVideoFilterBuilder(&opts).
+		WithWindowBar(2).
+		WithMarginFill(3).
+		Build(), " ")
+
+	for _, want := range []string{"loop=-1,fps=60[loopbar]", ",fps=60[bg]"} {
+		if !strings.Contains(got, want) {
+			t.Errorf("filter_complex missing %q\ngot: %s", want, got)
+		}
+	}
+}
+
+// Screenshots have no framerate; an fps filter there would be `fps=0`.
+func TestScreenshotOmitsFramerate(t *testing.T) {
+	style := DefaultStyleOptions()
+	style.WindowBar = "Colorful"
+
+	got := strings.Join(NewScreenshotFilterComplexBuilder(style).
+		WithWindowBar(2).
+		WithMarginFill(3).
+		Build(), " ")
+
+	if strings.Contains(got, "fps=") {
+		t.Errorf("screenshot filter should not set fps, got: %s", got)
+	}
+}