av/codec/h264/h264dec/decode.go

/*
DESCRIPTION
  decode.go provides slice decoding functionality.

AUTHORS
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  Copyright (C) 2019 the Australian Ocean Lab (AusOcean).

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package h264dec

// 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.
func picOrderCntType0(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.currPic.isIDR {
		panic("not implemented")
	}

	switch {
	case (ctx.PicOrderCntLsb < prevPicOrderCntLsb) && ((prevPicOrderCntLsb - ctx.PicOrderCntLsb) >= (vid.maxPicOrderCntLsb / 2)):
		vid.picOrderCntMsb = prevPicOrderCntMsb + vid.maxPicOrderCntLsb
	case (ctx.PicOrderCntLsb > prevPicOrderCntLsb) && ((ctx.PicOrderCntLsb - prevPicOrderCntLsb) > (vid.maxPicOrderCntLsb / 2)):
		vid.picOrderCntMsb = prevPicOrderCntMsb - vid.maxPicOrderCntLsb
	default:
		vid.picOrderCntMsb = prevPicOrderCntMsb
	}

	if !vid.currPic.isBottomField {
		topFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
	}

	if !vid.currPic.isTopField {
		if !ctx.FieldPic {
			bottomFieldOrderCnt = topFieldOrderCnt + ctx.DeltaPicOrderCntBottom
		} else {
			bottomFieldOrderCnt = vid.picOrderCntMsb + ctx.PicOrderCntLsb
		}
	}
	return
}