diff --git a/codec/h264/h264dec/decode.go b/codec/h264/h264dec/decode.go
index 22cfc181..d4d929e2 100644
--- a/codec/h264/h264dec/decode.go
+++ b/codec/h264/h264dec/decode.go
@@ -23,3 +23,169 @@ 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 decodePicOrderCntType0(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+	prevPicOrderCntMsb, prevPicOrderCntLsb := 0, 0
+	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
+
+	// NB: We're currently only handling IDRs so panic.
+	if !vid.idrPicFlag {
+		panic("not implemented")
+	}
+
+	vid.picOrderCntMsb = prevPicOrderCntMsb
+	if ctx.PicOrderCntLsb < prevPicOrderCntLsb && (prevPicOrderCntLsb-ctx.PicOrderCntLsb) >= (vid.maxPicOrderCntLsb/2) {
+		vid.picOrderCntMsb = prevPicOrderCntMsb + vid.maxPicOrderCntLsb
+	} else if ctx.PicOrderCntLsb > prevPicOrderCntLsb && (ctx.PicOrderCntLsb-prevPicOrderCntLsb) > (vid.maxPicOrderCntLsb/2) {
+		vid.picOrderCntMsb = prevPicOrderCntMsb - vid.maxPicOrderCntLsb
+	}
+
+	if !ctx.BottomField {
+		topFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
+	} else if ctx.FieldPic {
+		bottomFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
+	} else {
+		bottomFieldOrderCnt = topFieldOrderCnt + ctx.DeltaPicOrderCntBottom
+	}
+	return
+}
+
+// picOrderCntType1 is used to return topFieldOrderCnt and bottomFieldOrderCnt
+// 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 decodePicOrderCntType1(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
+
+	// TODO: this will be prevFrameNum when we do frames other than IDR.
+	_ = vid.priorPic.FrameNum
+
+	if !vid.idrPicFlag {
+		panic("not implemented")
+	}
+
+	vid.frameNumOffset = 0
+
+	absFrameNum := 0
+	if ctx.NumRefFramesInPicOrderCntCycle != 0 {
+		absFrameNum = vid.frameNumOffset + ctx.FrameNum
+	}
+
+	if ctx.RefIdc == 0 && absFrameNum > 0 {
+		absFrameNum = absFrameNum - 1
+	}
+
+	var expectedPicOrderCnt int
+	if absFrameNum > 0 {
+		picOrderCntCycleCnt := (absFrameNum - 1) / int(ctx.NumRefFramesInPicOrderCntCycle)
+		frameNumInPicOrderCntCycle := (absFrameNum - 1) % int(ctx.NumRefFramesInPicOrderCntCycle)
+		expectedPicOrderCnt = picOrderCntCycleCnt * vid.expectedDeltaPerPicOrderCntCycle
+		for i := 0; i <= frameNumInPicOrderCntCycle; i++ {
+			expectedPicOrderCnt = expectedPicOrderCnt + ctx.OffsetForRefFrameList[i]
+		}
+	}
+
+	if ctx.RefIdc == 0 {
+		expectedPicOrderCnt = expectedPicOrderCnt + int(ctx.OffsetForNonRefPic)
+	}
+
+	if !ctx.FieldPic {
+		topFieldOrderCnt = expectedPicOrderCnt + ctx.DeltaPicOrderCnt[0]
+		bottomFieldOrderCnt = topFieldOrderCnt + int(ctx.OffsetForTopToBottomField) + ctx.DeltaPicOrderCnt[1]
+	} else if ctx.BottomField {
+		bottomFieldOrderCnt = expectedPicOrderCnt + int(ctx.OffsetForTopToBottomField) + ctx.DeltaPicOrderCnt[0]
+	} else {
+		topFieldOrderCnt = expectedPicOrderCnt + ctx.DeltaPicOrderCnt[0]
+	}
+	return
+}
+
+// picOrderCntType2 is used to return topFieldOrderCnt and bottomFieldOrderCnt
+// 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 decodePicOrderCntType2(vid *VideoStream, ctx *SliceContext) (topFieldOrderCnt, bottomFieldOrderCnt int) {
+	topFieldOrderCnt, bottomFieldOrderCnt = -1, -1
+
+	// TODO: this will be prevFrameNum when we do frames other than IDR.
+	_ = vid.priorPic.FrameNum
+
+	if !vid.idrPicFlag {
+		panic("not implemented")
+	}
+	vid.frameNumOffset = 0
+
+	// TODO: handle tempPicOrderCnt calculation for when not IDR.
+	var tempPicOrderCnt int
+
+	if !ctx.FieldPic {
+		topFieldOrderCnt = tempPicOrderCnt
+		bottomFieldOrderCnt = tempPicOrderCnt
+	} else if ctx.BottomField {
+		bottomFieldOrderCnt = tempPicOrderCnt
+	} else {
+		topFieldOrderCnt = tempPicOrderCnt
+	}
+
+	return
+}
diff --git a/codec/h264/h264dec/slice.go b/codec/h264/h264dec/slice.go
index 5ffcf5fd..26a92642 100644
--- a/codec/h264/h264dec/slice.go
+++ b/codec/h264/h264dec/slice.go
@@ -35,15 +35,33 @@ const (
 	chroma444
 )
 
+type picture struct {
+	*SliceContext
+	isIDR         bool
+	isBottomField bool
+	isTopField    bool
+}
+
 type VideoStream struct {
 	*SPS
 	*PPS
 	Slices []*SliceContext
 
-	ChromaArrayType int
+	ChromaArrayType                  int
+	priorPic                         *picture
+	currPic                          *picture
+	maxPicOrderCntLsb                int
+	picOrderCntMsb                   int
+	idrPicFlag                       bool
+	frameNumOffset                   int
+	expectedDeltaPerPicOrderCntCycle int
+	topFieldOrderCnt                 int
+	bottomFieldOrderCnt              int
 }
 
 type SliceContext struct {
+	*SPS
+	*PPS
 	*NALUnit
 	*Slice
 	chromaArrayType int