mirror of https://bitbucket.org/ausocean/av.git
130 lines
3.3 KiB
Go
130 lines
3.3 KiB
Go
/*
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DESCRIPTION
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cavlc.go provides utilities for context-adaptive variable-length coding
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for the parsing of H.264 syntax structure fields.
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AUTHORS
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Saxon A. Nelson-Milton <saxon@ausocean.org>
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LICENSE
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Copyright (C) 2019 the Australian Ocean Lab (AusOcean).
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package h264dec
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import (
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"errors"
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"fmt"
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"bitbucket.org/ausocean/av/codec/h264/h264dec/bits"
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)
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// parseLevelPrefix parses the level_prefix variable as specified by the process
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// outlined in section 9.2.2.1 in the specifications.
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func parseLevelPrefix(br *bits.BitReader) (int, error) {
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zeros := -1
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for b := 0; b != 1; zeros++ {
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_b, err := br.ReadBits(1)
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if err != nil {
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return -1, fmt.Errorf("could not read bit, failed with error: %v", err)
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}
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b = int(_b)
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}
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return zeros, nil
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}
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// parseLevelInformation parses level information and returns the resultant
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// levelVal list using the process defined by section 9.2.2 in the specifications.
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func parseLevelInformation(br *bits.BitReader, totalCoeff, trailingOnes int) ([]int, error) {
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var levelVal []int
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var i int
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for ; i < trailingOnes; i++ {
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b, err := br.ReadBits(1)
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if err != nil {
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return nil, fmt.Errorf("could not read trailing_ones_sign_flag, failed with error: %v", err)
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}
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levelVal = append(levelVal, 1-int(b)*2)
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}
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var suffixLen int
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switch {
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case totalCoeff > 10 && trailingOnes < 3:
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suffixLen = 1
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case totalCoeff <= 10 || trailingOnes == 3:
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suffixLen = 0
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default:
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return nil, errors.New("invalid TotalCoeff and TrailingOnes combination")
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}
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for j := 0; j < totalCoeff-trailingOnes; j++ {
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levelPrefix, err := parseLevelPrefix(br)
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if err != nil {
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return nil, fmt.Errorf("could not parse level prefix, failed with error: %v", err)
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}
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var levelSuffixSize int
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switch {
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case levelPrefix == 14 && suffixLen == 0:
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levelSuffixSize = 4
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case levelPrefix >= 15:
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levelSuffixSize = levelPrefix - 3
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default:
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levelSuffixSize = suffixLen
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}
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var levelSuffix int
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if levelSuffixSize > 0 {
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b, err := br.ReadBits(levelSuffixSize)
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if err != nil {
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return nil, fmt.Errorf("could not parse levelSuffix, failed with error: %v", err)
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}
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levelSuffix = int(b)
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} else {
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levelSuffix = 0
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}
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levelCode := (mini(15, levelPrefix) << uint(suffixLen)) + levelSuffix
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if levelPrefix >= 15 && suffixLen == 0 {
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levelCode += 15
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}
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if levelPrefix >= 16 {
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levelCode += (1 << uint(levelPrefix-3)) - 4096
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}
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if i == trailingOnes && trailingOnes < 3 {
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levelCode += 2
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}
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if levelCode%2 == 0 {
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levelVal = append(levelVal, (levelCode+2)>>1)
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} else {
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levelVal = append(levelVal, (-levelCode-1)>>1)
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}
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if suffixLen == 0 {
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suffixLen = 1
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}
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if absi(levelVal[i]) > (3<<uint(suffixLen-1)) && suffixLen < 6 {
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suffixLen++
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}
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i++
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}
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return levelVal, nil
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}
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