Properly preserve entry count on context.

box_types_metadata.go

@@ -1,10 +1,8 @@
 package mp4
 
 import (
-	"encoding/binary"
 	"fmt"
 
-	"github.com/abema/go-mp4/internal/bitio"
 	"github.com/abema/go-mp4/internal/util"
 )
 
@@ -226,20 +224,6 @@ func (k *Keys) GetFieldLength(name string, ctx Context) uint {
 	panic(fmt.Errorf("invalid name of dynamic-length field: boxType=keys fieldName=%s", name))
 }
 
-func (k *Keys) OnReadField(name string, r bitio.ReadSeeker, leftBits uint64, ctx Context) (rbits uint64, override bool, err error) {
-	switch name {
-	// Override EntryCount unmarshaller so we can set QuickTimeKeysMetaEntryCount on Context
-	case "EntryCount":
-		err = binary.Read(r, binary.BigEndian, &k.EntryCount)
-		ctx.QuickTimeKeysMetaEntryCount = int(k.EntryCount)
-		override = true
-		rbits += uint64(32)
-		return
-	default:
-		return
-	}
-}
-
 /*************************** key ****************************/
 
 // Key is a key value field in the Keys BoxType

read.go

@@ -64,6 +64,18 @@ func readBoxStructureFromInternal(r io.ReadSeeker, bi *BoxInfo, path BoxPath, ha
 		}
 	}
 
+	// parse numbered ilst items after keys box by saving EntryCount field to context
+	if bi.Type == BoxTypeKeys() {
+		var keys Keys
+		if _, err := Unmarshal(r, bi.Size-bi.HeaderSize, &keys, bi.Context); err != nil {
+			return nil, err
+		}
+		bi.QuickTimeKeysMetaEntryCount = int(keys.EntryCount)
+		if _, err := bi.SeekToPayload(r); err != nil {
+			return nil, err
+		}
+	}
+
 	ctx := bi.Context
 	if bi.Type == BoxTypeWave() {
 		ctx.UnderWave = true
@@ -172,6 +184,11 @@ func readBoxStructure(r io.ReadSeeker, totalSize uint64, isRoot bool, path BoxPa
 		if bi.IsQuickTimeCompatible {
 			ctx.IsQuickTimeCompatible = true
 		}
+
+		// preserve keys entry count on context for subsequent ilst number item box
+		if bi.Type == BoxTypeKeys() {
+			ctx.QuickTimeKeysMetaEntryCount = bi.QuickTimeKeysMetaEntryCount
+		}
 	}
 
 	if totalSize != 0 && !ctx.IsQuickTimeCompatible {