From 2ccceedda951b28eca118bd865d150959e4934b5 Mon Sep 17 00:00:00 2001
From: Martin Riedl <martin.riedl.92@googlemail.com>
Date: Thu, 17 Oct 2024 18:05:07 +0200
Subject: [PATCH] new fixed datatypes

---
 Fixed.go          | 69 +++++++++++++++++++++++++++++++++++++++++++++++
 MovieHeaderBox.go |  8 +++---
 2 files changed, 73 insertions(+), 4 deletions(-)
 create mode 100644 Fixed.go

diff --git a/Fixed.go b/Fixed.go
new file mode 100644
index 0000000..d47a912
--- /dev/null
+++ b/Fixed.go
@@ -0,0 +1,69 @@
+// 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"
+
+type Fixed88 struct {
+	b []byte
+}
+
+func NewFixed88ByBytes(b []byte) Fixed88 {
+	return Fixed88{
+		b: b,
+	}
+}
+
+func (fixed Fixed88) ToUInt16() uint16 {
+	return uint16(fixed.b[0])
+}
+
+func (fixed Fixed88) ToFloat32() float32 {
+	var result float32 = 0
+
+	a := uint16(fixed.b[0])
+	b := uint16(fixed.b[1])
+
+	result += float32(a)
+	result += float32(b) / 1_000 // max of uint8 is 255
+
+	return result
+}
+
+type Fixed1616 struct {
+	b []byte
+}
+
+func NewFixed1616ByBytes(b []byte) Fixed1616 {
+	return Fixed1616{
+		b: b,
+	}
+}
+
+func (fixed Fixed1616) ToUInt16() uint16 {
+	return binary.BigEndian.Uint16(fixed.b[0:2])
+}
+
+func (fixed Fixed1616) ToFloat32() float32 {
+	var result float32 = 0
+
+	a := binary.BigEndian.Uint16(fixed.b[0:2])
+	b := binary.BigEndian.Uint16(fixed.b[2:4])
+
+	result += float32(a)
+	result += float32(b) / 100_000 // max of uint16 is 65535
+
+	return result
+}
diff --git a/MovieHeaderBox.go b/MovieHeaderBox.go
index 1d31f55..680ff6f 100644
--- a/MovieHeaderBox.go
+++ b/MovieHeaderBox.go
@@ -58,10 +58,10 @@ type MovieHeaderBox struct {
 	DurationV1 uint64
 	// is a fixed point 16.16 number that indicates the preferred rate to play the presentation; 1.0
 	// (0x00010000) is normal forward playback
-	Rate int32
+	Rate Fixed1616
 	// is a fixed point 8.8 number that indicates the preferred playback volume. 1.0 (0x0100) is
 	// full volume.
-	Volume int16
+	Volume Fixed88
 	// provides a transformation matrix for the video; (u,v,w) are restricted here to (0,0,1), hex
 	// values (0,0,0x40000000).
 	Matrix []int32
@@ -94,8 +94,8 @@ func ParseMovieHeaderBox(filePosition uint64, headerSize uint32, content []byte)
 		position += 16
 	}
 
-	box.Rate = int32(binary.BigEndian.Uint32(content[position : position+4]))
-	box.Volume = int16(binary.BigEndian.Uint16(content[position+4 : position+6]))
+	box.Rate = NewFixed1616ByBytes(content[position : position+4])
+	box.Volume = NewFixed88ByBytes(content[position+4 : position+6])
 	position += 4 + 2 + 2 + 8 // 4 bytes for rate, 2 bytes for volume, 2 bytes reserved and 8 bytes reserved
 	for i := 0; i < 9; i++ {
 		box.Matrix = append(box.Matrix, int32(binary.BigEndian.Uint32(content[position:position+4])))