add synchronous video frame bridge

internal/playback/video_bridge.go

@@ -0,0 +1,60 @@
+package playback
+
+import (
+	"context"
+	"sync"
+)
+
+type PendingVideoFrame struct {
+	Frame VideoFrame
+
+	completeOnce sync.Once
+	result       chan error
+}
+
+type VideoBridge struct {
+	requests chan *PendingVideoFrame
+}
+
+func NewVideoBridge() *VideoBridge {
+	return &VideoBridge{
+		requests: make(chan *PendingVideoFrame),
+	}
+}
+
+func (b *VideoBridge) ConsumeVideo(
+	ctx context.Context,
+	frame VideoFrame,
+) error {
+	pending := &PendingVideoFrame{
+		Frame:  frame,
+		result: make(chan error, 1),
+	}
+
+	select {
+	case b.requests <- pending:
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+
+	// The render thread now owns temporary access to the borrowed payload.
+	// We must wait for Complete even if ctx is canceled.
+	return <-pending.result
+}
+
+func (b *VideoBridge) Next(
+	ctx context.Context,
+) (*PendingVideoFrame, error) {
+	select {
+	case pending := <-b.requests:
+		return pending, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+func (f *PendingVideoFrame) Complete(err error) {
+	f.completeOnce.Do(func() {
+		f.result <- err
+	})
+}