From ca8bedd8d314864438176874341f3d8cd1ba572e Mon Sep 17 00:00:00 2001
From: Martin Riedl <martin.riedl.92@googlemail.com>
Date: Fri, 27 Dec 2024 18:39:52 +0100
Subject: [PATCH] feat: track extends box

---
 README.md          |  2 +-
 TrackExtendsBox.go | 60 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 TrackExtendsBox.go

diff --git a/README.md b/README.md
index e48f07b..230cee8 100644
--- a/README.md
+++ b/README.md
@@ -58,7 +58,7 @@ Implementation progress of ISO/IEC 14496-12:2015:
 | 8.7.9 Sample Auxiliary Information Offsets Box     | saio           |      - |
 | 8.8.1 Movie Extends Box                            | mvex           |   100% |
 | 8.8.2 Movie Extends Header Box                     | mehd           |      - |
-| 8.8.3 Track Extends Box                            | trex           |      - |
+| 8.8.3 Track Extends Box                            | trex           |   100% |
 | 8.8.4 Movie Fragment Box                           | moof           |   100% |
 | 8.8.5 Movie Fragment Header Box                    | mfhd           |   100% |
 | 8.8.6 Track Fragment Box                           | traf           |   100% |
diff --git a/TrackExtendsBox.go b/TrackExtendsBox.go
new file mode 100644
index 0000000..47994ee
--- /dev/null
+++ b/TrackExtendsBox.go
@@ -0,0 +1,60 @@
+// Copyright 2024 Martin Riedl
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package gomp4
+
+import (
+	"encoding/binary"
+)
+
+// TrackExtendsBox Track Extends Box struct
+//
+// 8.8.3 Track Extends Box
+//
+// This sets up default values used by the movie fragments. By setting defaults in this way, space and
+// complexity can be saved in each Track Fragment Box.
+type TrackExtendsBox struct {
+	*FullBox
+	// identifies the track; this shall be the track ID of a track in the Movie Box
+	TrackID                       uint32
+	DefaultSampleDescriptionIndex uint32
+	DefaultSampleDuration         uint32
+	DefaultSampleSize             uint32
+	DefaultSampleFlags            uint32
+}
+
+const BoxTypeTrackExtends = "trex"
+
+func init() {
+	BoxDefinitions = append(BoxDefinitions, BoxDefinition{
+		Type:        BoxTypeTrackExtends,
+		ParentTypes: []string{BoxTypeMovieExtends},
+		Parser:      ParseTrackExtendsBox,
+	})
+}
+
+// ParseTrackExtendsBox creates a new track extends box struct based on bytes
+func ParseTrackExtendsBox(parser *Parser, filePosition uint64, headerSize uint32, content []byte) (any, error) {
+	box := &TrackExtendsBox{
+		FullBox: newFullBox(&Box{filePosition, headerSize}, content[0:4]),
+	}
+
+	box.TrackID = binary.BigEndian.Uint32(content[4:8])
+	box.DefaultSampleDescriptionIndex = binary.BigEndian.Uint32(content[8:12])
+	box.DefaultSampleDuration = binary.BigEndian.Uint32(content[12:16])
+	box.DefaultSampleSize = binary.BigEndian.Uint32(content[16:20])
+	box.DefaultSampleFlags = binary.BigEndian.Uint32(content[20:24])
+
+	return box, nil
+}