add bounded video source read

internal/source/source.go

@@ -120,15 +120,43 @@ func (s *Source) Close() error {
 
 func (s *Source) NextCtx(ctx context.Context, timeout time.Duration) (Frame, error) {
 	for {
+		frame, err := s.ReadOnceCtx(ctx, timeout)
+		if err == nil {
+			return frame, nil
+		}
+		if ctx.Err() != nil {
+			return Frame{}, ctx.Err()
+		}
+		if KindOf(err) != ErrorKindTemporary {
+			return Frame{}, err
+		}
+
+		if errors.Is(err, mxl.ErrOutOfRangeEarly) {
 			select {
+			case <-time.After(10 * time.Millisecond):
 			case <-ctx.Done():
 				return Frame{}, ctx.Err()
-		default:
 			}
+		}
+	}
+}
+
+func (s *Source) ReadOnceCtx(
+	ctx context.Context,
+	timeout time.Duration,
+) (Frame, error) {
+	if err := ctx.Err(); err != nil {
+		return Frame{}, err
+	}
+
 	g, err := s.reader.GetGrain(s.idx, timeout)
+	if ctx.Err() != nil {
+		return Frame{}, ctx.Err()
+	}
+
 	switch {
 	case err == nil:
-			f := Frame{
+		frame := Frame{
 			Index:   g.Index,
 			Width:   s.width,
 			Height:  s.height,
@@ -138,16 +166,44 @@ func (s *Source) NextCtx(ctx context.Context, timeout time.Duration) (Frame, err
 			Payload: g.Payload,
 		}
 		s.idx++
-			return f, nil
+		return frame, nil
+
 	case errors.Is(err, mxl.ErrTimeout):
 		s.idx = mxl.CurrentIndex(s.rate)
+		return Frame{}, wrapError(
+			"read video",
+			ErrorKindTemporary,
+			err,
+		)
+
 	case errors.Is(err, mxl.ErrOutOfRangeEarly):
-			time.Sleep(10 * time.Millisecond)
+		return Frame{}, wrapError(
+			"read video",
+			ErrorKindTemporary,
+			err,
+		)
+
 	case errors.Is(err, mxl.ErrOutOfRangeLate):
 		s.idx = mxl.CurrentIndex(s.rate)
+		return Frame{}, wrapError(
+			"read video",
+			ErrorKindTemporary,
+			err,
+		)
+
+	case errors.Is(err, mxl.ErrFlowInvalid):
+		return Frame{}, wrapError(
+			"read video",
+			ErrorKindUnavailable,
+			err,
+		)
+
 	default:
-			return Frame{}, fmt.Errorf("GetGrain: %w", err)
-		}
+		return Frame{}, wrapError(
+			"read video",
+			ErrorKindUnavailable,
+			err,
+		)
 	}
 }