Merged in level-information (pull request #245)

codec/h264/h264dec: add function for parsing level information using process in section 9.2.2 of specifications

Approved-by: Alan Noble <anoble@gmail.com>

codec/h264/h264dec/cavlc.go

@@ -26,6 +26,7 @@ LICENSE
 package h264dec
 
 import (
+	"errors"
 	"fmt"
 
 	"bitbucket.org/ausocean/av/codec/h264/h264dec/bits"
@@ -44,3 +45,85 @@ func parseLevelPrefix(br *bits.BitReader) (int, error) {
 	}
 	return zeros, nil
 }
+
+// parseLevelInformation parses level information and returns the resultant
+// levelVal list using the process defined by section 9.2.2 in the specifications.
+func parseLevelInformation(br *bits.BitReader, totalCoeff, trailingOnes int) ([]int, error) {
+	var levelVal []int
+	var i int
+	for ; i < trailingOnes; i++ {
+		b, err := br.ReadBits(1)
+		if err != nil {
+			return nil, fmt.Errorf("could not read trailing_ones_sign_flag, failed with error: %v", err)
+		}
+		levelVal = append(levelVal, 1-int(b)*2)
+	}
+
+	var suffixLen int
+	switch {
+	case totalCoeff > 10 && trailingOnes < 3:
+		suffixLen = 1
+	case totalCoeff <= 10 || trailingOnes == 3:
+		suffixLen = 0
+	default:
+		return nil, errors.New("invalid TotalCoeff and TrailingOnes combination")
+	}
+
+	for j := 0; j < totalCoeff-trailingOnes; j++ {
+		levelPrefix, err := parseLevelPrefix(br)
+		if err != nil {
+			return nil, fmt.Errorf("could not parse level prefix, failed with error: %v", err)
+		}
+
+		var levelSuffixSize int
+		switch {
+		case levelPrefix == 14 && suffixLen == 0:
+			levelSuffixSize = 4
+		case levelPrefix >= 15:
+			levelSuffixSize = levelPrefix - 3
+		default:
+			levelSuffixSize = suffixLen
+		}
+
+		var levelSuffix int
+		if levelSuffixSize > 0 {
+			b, err := br.ReadBits(levelSuffixSize)
+			if err != nil {
+				return nil, fmt.Errorf("could not parse levelSuffix, failed with error: %v", err)
+			}
+			levelSuffix = int(b)
+		} else {
+			levelSuffix = 0
+		}
+
+		levelCode := (mini(15, levelPrefix) << uint(suffixLen)) + levelSuffix
+
+		if levelPrefix >= 15 && suffixLen == 0 {
+			levelCode += 15
+		}
+
+		if levelPrefix >= 16 {
+			levelCode += (1 << uint(levelPrefix-3)) - 4096
+		}
+
+		if i == trailingOnes && trailingOnes < 3 {
+			levelCode += 2
+		}
+
+		if levelCode%2 == 0 {
+			levelVal = append(levelVal, (levelCode+2)>>1)
+		} else {
+			levelVal = append(levelVal, (-levelCode-1)>>1)
+		}
+
+		if suffixLen == 0 {
+			suffixLen = 1
+		}
+
+		if absi(levelVal[i]) > (3<<uint(suffixLen-1)) && suffixLen < 6 {
+			suffixLen++
+		}
+		i++
+	}
+	return levelVal, nil
+}