Implement ReadTimingInfo, it is needed in ReadUncompressedFrameHeader() when IsReducedStillPictureHeader is false

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuFrameHeader.cs

@@ -71,6 +71,8 @@ internal class ObuFrameHeader
 
     internal bool ShowableFrame { get; set; }
 
+    internal uint FrameToShowMapIdx { get; set; }
+
     internal bool ErrorResilientMode { get; set; }
 
     internal bool AllowScreenContentTools { get; set; }

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuOperatingPoint.cs

@@ -11,7 +11,7 @@ internal class ObuOperatingPoint
 
     internal int SequenceTier { get; set; }
 
-    internal bool IsDecoderModelPresent { get; set; }
+    internal bool IsDecoderModelInfoPresent { get; set; }
 
     internal bool IsInitialDisplayDelayPresent { get; set; }
 

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuReader.cs

@@ -281,7 +281,7 @@ internal class ObuReader
             }
 
             operatingPoint.SequenceTier = 0;
-            operatingPoint.IsDecoderModelPresent = false;
+            operatingPoint.IsDecoderModelInfoPresent = false;
             operatingPoint.IsInitialDisplayDelayPresent = false;
         }
         else
@@ -289,11 +289,16 @@ internal class ObuReader
             sequenceHeader.TimingInfoPresentFlag = reader.ReadBoolean();
             if (sequenceHeader.TimingInfoPresentFlag)
             {
+                ReadTimingInfo(ref reader,  sequenceHeader);
                 sequenceHeader.DecoderModelInfoPresentFlag = reader.ReadBoolean();
                 if (sequenceHeader.DecoderModelInfoPresentFlag)
                 {
                     ReadDecoderModelInfo(ref reader, sequenceHeader);
                 }
+                else
+                {
+                    sequenceHeader.DecoderModelInfoPresentFlag = false;
+                }
             }
 
             sequenceHeader.InitialDisplayDelayPresentFlag = reader.ReadBoolean();
@@ -315,15 +320,15 @@ internal class ObuReader
 
                 if (sequenceHeader.DecoderModelInfoPresentFlag)
                 {
-                    sequenceHeader.OperatingPoint[i].IsDecoderModelPresent = reader.ReadBoolean();
-                    if (sequenceHeader.OperatingPoint[i].IsDecoderModelPresent)
+                    sequenceHeader.OperatingPoint[i].IsDecoderModelInfoPresent = reader.ReadBoolean();
+                    if (sequenceHeader.OperatingPoint[i].IsDecoderModelInfoPresent)
                     {
                         // TODO: operating_parameters_info( i )
                     }
                 }
                 else
                 {
-                    sequenceHeader.OperatingPoint[i].IsDecoderModelPresent = false;
+                    sequenceHeader.OperatingPoint[i].IsDecoderModelInfoPresent = false;
                 }
 
                 if (sequenceHeader.InitialDisplayDelayPresentFlag)
@@ -543,6 +548,24 @@ internal class ObuReader
         FramePresentationTimeLength = reader.ReadLiteral(5) + 1
     };
 
+    /// <summary>
+    /// 5.5.3. Timing info syntax.
+    /// </summary>
+    private static void ReadTimingInfo(ref Av1BitStreamReader reader, ObuSequenceHeader sequenceHeader)
+    {
+        sequenceHeader.TimingInfo = new ObuTimingInfo
+        {
+            NumUnitsInDisplayTick = reader.ReadLiteral(32),
+            TimeScale = reader.ReadLiteral(32),
+            EqualPictureInterval = reader.ReadBoolean()
+        };
+
+        if (sequenceHeader.TimingInfo.EqualPictureInterval)
+        {
+            sequenceHeader.TimingInfo.NumTicksPerPicture = reader.ReadUnsignedVariableLength() + 1;
+        }
+    }
+
     private static void ReadBitDepth(ref Av1BitStreamReader reader, ObuColorConfig colorConfig, ObuSequenceHeader sequenceHeader)
     {
         bool hasHighBitDepth = reader.ReadBoolean();
@@ -863,6 +886,16 @@ internal class ObuReader
             frameInfo.ShowableFrame = false;
             frameInfo.ErrorResilientMode = true;
         }
+        else
+        {
+            frameInfo.ShowExistingFrame = reader.ReadBoolean();
+            if (frameInfo.ShowExistingFrame)
+            {
+                frameInfo.FrameToShowMapIdx = reader.ReadLiteral(3);
+            }
+
+            // TODO: There is still some parts not implemented here
+        }
 
         if (frameInfo.FrameType == ObuFrameType.KeyFrame && frameInfo.ShowFrame)
         {

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuSequenceHeader.cs

@@ -25,7 +25,7 @@ internal class ObuSequenceHeader
 
     public bool TimingInfoPresentFlag { get; set; }
 
-    public object? TimingInfo { get; set; }
+    public ObuTimingInfo? TimingInfo { get; set; }
 
     public bool IsFrameIdNumbersPresent { get; set; }
 

src/ImageSharp/Formats/Heif/Av1/OpenBitstreamUnit/ObuTimingInfo.cs

@@ -0,0 +1,33 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
+
+internal class ObuTimingInfo
+{
+    /// <summary>
+    /// Gets or sets NumUnitsInDisplayTick. NumUnitsInDisplayTick is the number of time units of a clock operating at the frequency TimeScale Hz that
+    /// corresponds to one increment of a clock tick counter. A display clock tick, in seconds, is equal to
+    /// NumUnitsInDisplayTick divided by TimeScale.
+    /// </summary>
+    public uint NumUnitsInDisplayTick { get; set; }
+
+    /// <summary>
+    /// Gets or sets TimeScale. TimeScale is the number of time units that pass in one second.
+    /// It is a requirement of bitstream conformance that TimeScale is greater than 0.
+    /// </summary>
+    public uint TimeScale { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether that pictures should be displayed according to their output order with the
+    /// number of ticks between two consecutive pictures (without dropping frames) specified by NumTicksPerPicture.
+    /// EqualPictureInterval equal to false indicates that the interval between two consecutive pictures is not specified.
+    /// </summary>
+    public bool EqualPictureInterval { get; set; }
+
+    /// <summary>
+    /// Gets or sets NumTicksPerPicture. NumTicksPerPicture specifies the number of clock ticks corresponding to output time between two
+    /// consecutive pictures in the output order.
+    /// </summary>
+    public uint NumTicksPerPicture { get; set; }
+}