codec/h264/264dec/decode.go: added decodePicOrderCnt to return topFieldOrderCnt and bottomFieldOrderCnt based on picOrderCntType

Also added placeholder for a general 'decode' function.

codec/h264/h264dec/decode.go

@@ -24,11 +24,67 @@ LICENSE
 
 package h264dec
 
+import (
+	"errors"
+	"fmt"
+)
+
+// NB: this is a placeholder.
+func decode(vid *VideoStream, ctx *SliceContext) error {
+	var err error
+	vid.topFieldOrderCnt, vid.bottomFieldOrderCnt, err = decodePicOrderCnt(vid, ctx)
+	if err != nil {
+		return fmt.Errorf("could not derive topFieldOrderCnt and bottomFieldOrderCnt, failed with error: %v", err)
+	}
+
+	// According to 8.2.1 after decoding picture.
+	if ctx.elements[0].MemoryManagementControlOperation == 5 {
+		tempPicOrderCnt := picOrderCnt(ctx)
+		vid.topFieldOrderCnt = vid.topFieldOrderCnt - tempPicOrderCnt
+		vid.bottomFieldOrderCnt = vid.bottomFieldOrderCnt - tempPicOrderCnt
+	}
+	return nil
+}
+
+// TODO: complete this. Unsure how to determine if pic is frame or a
+// complementary field pair.
+// picOrderCnt as defined by section 8.2.1.
+func picOrderCnt(ctx *SliceContext) int {
+	panic("not implemented")
+}
+
+// decodePicOrderCnt derives topFieldOrderCnt and bottomFieldOrderCnt based
+// on the PicOrderCntType using the process defined in section 8.2.1 of the
+// specifications.
+func decodePicOrderCnt(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int, err error) {
+	// There are some steps listed in 8.2.1 regarding cases when not an IDR frame,
+	// but we're not yet dealing with that.
+	// TODO: write steps dealing with not IDR frame.
+	if !vid.idrPicFlag {
+		panic("not implemented")
+	}
+
+	switch ctx.PicOrderCountType {
+	case 0:
+		topFieldOrderCnt, bottomFieldOrderCnt = decodePicOrderCntType0(vid, ctx)
+	case 1:
+		topFieldOrderCnt, bottomFieldOrderCnt = decodePicOrderCntType1(vid, ctx)
+	case 2:
+		topFieldOrderCnt, bottomFieldOrderCnt = decodePicOrderCntType2(vid, ctx)
+	default:
+		err = errors.New("invalid PicOrderCountType")
+	}
+
+	// TODO: check DiffPicOrderCnt( picA, picB ) once picOrderCnt( picX ) is
+	// worked out.
+	return
+}
+
 // picOrderCntType0 is used to return topFieldOrderCnt and bottomFieldOrderCnt
 // when pic_order_cnt_type i.e vid.PicOrderCntType == 0, using the process
 // defined in section 8.2.1.1 of the specifications. If topFieldOrderCnt or
 // bottomFieldOrderCnt are -1 they are unset.
-func picOrderCntType0(vid *VideoStream, ctx SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+func decodePicOrderCntType0(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
 	prevPicOrderCntMsb, prevPicOrderCntLsb := 0, 0
 	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
 
@@ -62,7 +118,7 @@ func picOrderCntType0(vid *VideoStream, ctx SliceContext) (topFieldOrderCnt, bot
 // when vic.PicOrderCntType == 1 according to logic defined in section 8.2.1.2
 // of the specifications. If topFieldOrderCnt or bottomFieldOrderCnt are -1,
 // then they are considered unset.
-func picOrderCntType1(vid VideoStream, ctx SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+func decodePicOrderCntType1(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
 	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
 
 	// TODO: this will be prevFrameNum when we do frames other than IDR.
@@ -113,7 +169,7 @@ func picOrderCntType1(vid VideoStream, ctx SliceContext) (topFieldOrderCnt, bott
 // when vic.PicOrderCntType == 1 according to logic defined in section 8.2.1.3
 // of the specifications. If topFieldOrderCnt or bottomFieldOrderCnt are -1,
 // then they are considered unset.
-func picOrderCntType2(vid VideoStream, ctx SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+func decodePicOrderCntType2(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
 	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
 
 	// TODO: this will be prevFrameNum when we do frames other than IDR.

codec/h264/h264dec/slice.go

@@ -55,6 +55,8 @@ type VideoStream struct {
 	idrPicFlag                       bool
 	frameNumOffset                   int
 	expectedDeltaPerPicOrderCntCycle int
+	topFieldOrderCnt                 int
+	bottomFieldOrderCnt              int
 }
 
 type SliceContext struct {