From c0be9b1910055cb98c12c08a7ad3747866866c62 Mon Sep 17 00:00:00 2001
From: Saxon <saxon@ausocean.org>
Date: Mon, 9 Sep 2019 13:26:46 +0930
Subject: [PATCH] codec/h264/h264dec/decode.go: added picOrderCntType2 to
 derive topfieldOrderCnt and bottomFieldOrderCnt for when picOrderCntType == 2

---
 codec/h264/h264dec/decode.go | 38 ++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/codec/h264/h264dec/decode.go b/codec/h264/h264dec/decode.go
index b3ec42dc..19ae3aa0 100644
--- a/codec/h264/h264dec/decode.go
+++ b/codec/h264/h264dec/decode.go
@@ -108,3 +108,41 @@ func picOrderCntType1(vid VideoStream, ctx SliceContext) (topFieldOrderCnt, bott
 	}
 	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 picOrderCntType2(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 {
+		vid.frameNumOffset = 0
+	} else {
+		panic("not implemented")
+	}
+
+	var tempPicOrderCnt int
+	switch {
+	case vid.idrPicFlag:
+		tempPicOrderCnt = 0
+	case ctx.RefIdc == 0:
+		tempPicOrderCnt = 2*(vid.frameNumOffset+ctx.FrameNum) - 1
+	default:
+		tempPicOrderCnt = 2 * (vid.frameNumOffset + ctx.FrameNum)
+	}
+
+	switch {
+	case ctx.FieldPic:
+		topFieldOrderCnt = tempPicOrderCnt
+		bottomFieldOrderCnt = tempPicOrderCnt
+	case ctx.BottomField:
+		bottomFieldOrderCnt = tempPicOrderCnt
+	default:
+		topFieldOrderCnt = tempPicOrderCnt
+	}
+	return
+}