define synchronized playback contracts

internal/playback/sync.go

@@ -0,0 +1,34 @@
+package playback
+
+import "context"
+
+// SyncFrame contains one video frame and its corresponding audio batch.
+//
+// Both payloads may borrow reader-owned memory and are valid only until the
+// next ReadSync call or until the reader is closed.
+type SyncFrame struct {
+	Video VideoFrame
+	Audio AudioFrame
+}
+
+// SyncReader reads synchronized audio/video pairs.
+//
+// ReadSync must not be called again until both frame payloads have been
+// consumed.
+type SyncReader interface {
+	ReadSync(context.Context) (SyncFrame, error)
+	Close() error
+}
+
+// SyncReaderFactory opens one synchronized reader for two configured feeds.
+//
+// Native MXL implementations may require the feeds to use the same domain.
+// Future manual synchronization may support different domains behind another
+// implementation of this interface.
+type SyncReaderFactory interface {
+	OpenSync(
+		context.Context,
+		FeedConfig,
+		FeedConfig,
+	) (SyncReader, error)
+}