Document AV1 OBU data models

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

@@ -3,6 +3,9 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the position of chroma samples relative to luma samples.
+/// </summary>
 internal enum ObuChromoSamplePosition : byte
 {
     /// <summary>
@@ -11,12 +14,12 @@ internal enum ObuChromoSamplePosition : byte
     Unknown = 0,
 
     /// <summary>
-    /// Horizontally co-located with luma(0, 0) sample, between two vertical samples.
+    /// The chroma sample is horizontally co-located with the top-left luma sample and lies between two luma rows.
     /// </summary>
     Vertical = 1,
 
     /// <summary>
-    /// Co-located with luma(0, 0) sample
+    /// The chroma sample is co-located with the top-left luma sample.
     /// </summary>
     Colocated = 2,
 

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

@@ -3,10 +3,19 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the color configuration signaled by an AV1 sequence header.
+/// </summary>
 internal class ObuColorConfig
 {
+    /// <summary>
+    /// Stores whether the sequence uses a single monochrome plane.
+    /// </summary>
     private bool isMonochrome;
 
+    /// <summary>
+    /// Gets or sets a value indicating whether color-description syntax is present.
+    /// </summary>
     public bool IsColorDescriptionPresent { get; set; }
 
     /// <summary>
@@ -23,29 +32,62 @@ internal class ObuColorConfig
         get => this.isMonochrome;
         set
         {
+            // Plane count is derived from the monochrome flag throughout the decoder, so update
+            // both values atomically rather than allowing the two pieces of state to diverge.
             this.PlaneCount = value ? 1 : Av1Constants.MaxPlanes;
             this.isMonochrome = value;
         }
     }
 
+    /// <summary>
+    /// Gets or sets the color-primary chromaticities.
+    /// </summary>
     public ObuColorPrimaries ColorPrimaries { get; set; }
 
+    /// <summary>
+    /// Gets or sets the transfer characteristics.
+    /// </summary>
     public ObuTransferCharacteristics TransferCharacteristics { get; set; }
 
+    /// <summary>
+    /// Gets or sets the matrix coefficients used to derive luma and chroma components.
+    /// </summary>
     public ObuMatrixCoefficients MatrixCoefficients { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether samples use the full numeric range.
+    /// </summary>
     public bool ColorRange { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether chroma is subsampled horizontally.
+    /// </summary>
     public bool SubSamplingX { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether chroma is subsampled vertically.
+    /// </summary>
     public bool SubSamplingY { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the U and V planes use separate quantizer deltas.
+    /// </summary>
     public bool HasSeparateUvDelta { get; set; }
 
+    /// <summary>
+    /// Gets or sets the chroma sample position for vertically subsampled images.
+    /// </summary>
     public ObuChromoSamplePosition ChromaSamplePosition { get; set; }
 
+    /// <summary>
+    /// Gets or sets the encoded sample bit depth.
+    /// </summary>
     public Av1BitDepth BitDepth { get; set; }
 
+    /// <summary>
+    /// Gets the color format represented by the monochrome and chroma-subsampling flags.
+    /// </summary>
+    /// <returns>The corresponding AV1 color format.</returns>
     public Av1ColorFormat GetColorFormat()
     {
         Av1ColorFormat format = Av1ColorFormat.Yuv400;

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

@@ -3,19 +3,73 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the CICP color-primary chromaticities signaled by an AV1 sequence.
+/// </summary>
 internal enum ObuColorPrimaries
 {
-    None = 0,
+    /// <summary>
+    /// The reserved zero value.
+    /// </summary>
+    Reserved = 0,
+
+    /// <summary>
+    /// ITU-R BT.709 primaries.
+    /// </summary>
     Bt709 = 1,
+
+    /// <summary>
+    /// Unspecified primaries.
+    /// </summary>
     Unspecified = 2,
+
+    /// <summary>
+    /// ITU-R BT.470 System M primaries.
+    /// </summary>
     Bt470M = 4,
+
+    /// <summary>
+    /// ITU-R BT.470 System B and G primaries.
+    /// </summary>
     Bt470BG = 5,
+
+    /// <summary>
+    /// ITU-R BT.601 primaries.
+    /// </summary>
     Bt601 = 6,
+
+    /// <summary>
+    /// SMPTE 240M primaries.
+    /// </summary>
     Smpte240 = 7,
+
+    /// <summary>
+    /// Generic film primaries.
+    /// </summary>
     GenericFilm = 8,
+
+    /// <summary>
+    /// ITU-R BT.2020 and BT.2100 primaries.
+    /// </summary>
     Bt2020 = 9,
+
+    /// <summary>
+    /// SMPTE ST 428 CIE XYZ primaries.
+    /// </summary>
     Xyz = 10,
+
+    /// <summary>
+    /// SMPTE RP 431-2 primaries.
+    /// </summary>
     Smpte431 = 11,
+
+    /// <summary>
+    /// SMPTE EG 432-1 primaries.
+    /// </summary>
     Smpte432 = 12,
+
+    /// <summary>
+    /// EBU Tech. 3213-E primaries.
+    /// </summary>
     Ebu3213 = 22,
 }

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

@@ -3,13 +3,28 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the constrained directional enhancement filter parameters for an AV1 frame.
+/// </summary>
 internal class ObuConstraintDirectionalEnhancementFilterParameters
 {
+    /// <summary>
+    /// Gets or sets the number of bits used to select a filter-strength entry.
+    /// </summary>
     public int BitCount { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the filter damping value.
+    /// </summary>
     public int Damping { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the primary and secondary luma strengths for each filter entry.
+    /// </summary>
     public int[] YStrength { get; set; } = new int[16];
 
+    /// <summary>
+    /// Gets or sets the primary and secondary chroma strengths for each filter entry.
+    /// </summary>
     public int[] UvStrength { get; set; } = new int[16];
 }

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

@@ -3,6 +3,9 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1;
 
+/// <summary>
+/// Contains the field widths and decoding-clock units used by the AV1 decoder model.
+/// </summary>
 internal class ObuDecoderModelInfo
 {
     /// <summary>

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

@@ -3,11 +3,23 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the delta-quantizer or delta-loop-filter signaling parameters for an AV1 frame.
+/// </summary>
 internal class ObuDeltaParameters
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether per-block delta values are present.
+    /// </summary>
     public bool IsPresent { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the delta-value resolution.
+    /// </summary>
     public int Resolution { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether separate loop-filter deltas are signaled for multiple filter targets.
+    /// </summary>
     public bool IsMulti { get; internal set; }
 }

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

@@ -3,6 +3,9 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the parameters used to synthesize AV1 film grain for a decoded frame.
+/// </summary>
 internal class ObuFilmGrainParameters
 {
     /// <summary>

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

@@ -5,94 +5,228 @@ using SixLabors.ImageSharp.Formats.Heif.Av1.Transform;
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Stores the decoded syntax and derived state for one AV1 frame header.
+/// </summary>
 internal class ObuFrameHeader
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether motion vectors use integer-sample precision.
+    /// </summary>
     public bool ForceIntegerMotionVector { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether intra-block copy is permitted.
+    /// </summary>
     public bool AllowIntraBlockCopy { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether reference-frame motion vectors may be used.
+    /// </summary>
     public bool UseReferenceFrameMotionVectors { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether motion vectors may use high precision.
+    /// </summary>
     public bool AllowHighPrecisionMotionVector { get; set; }
 
+    /// <summary>
+    /// Gets or sets the decoded tile layout.
+    /// </summary>
     public ObuTileGroupHeader TilesInfo { get; set; } = new ObuTileGroupHeader();
 
+    /// <summary>
+    /// Gets or sets a value indicating whether every segment uses lossless coding.
+    /// </summary>
     public bool CodedLossless { get; set; }
 
+    /// <summary>
+    /// Gets or sets the lossless-coding flag for each segment.
+    /// </summary>
     public bool[] LosslessArray { get; set; } = new bool[Av1Constants.MaxSegmentCount];
 
+    /// <summary>
+    /// Gets or sets the frame quantization parameters.
+    /// </summary>
     public ObuQuantizationParameters QuantizationParameters { get; set; } = new ObuQuantizationParameters();
 
+    /// <summary>
+    /// Gets or sets the frame segmentation parameters.
+    /// </summary>
     public ObuSegmentationParameters SegmentationParameters { get; set; } = new ObuSegmentationParameters();
 
+    /// <summary>
+    /// Gets or sets a value indicating whether coding is lossless and no super-resolution scaling is applied.
+    /// </summary>
     public bool AllLossless { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether warped motion is permitted.
+    /// </summary>
     public bool AllowWarpedMotion { get; set; }
 
+    /// <summary>
+    /// Gets or sets the permitted reference prediction mode.
+    /// </summary>
     public ObuReferenceMode ReferenceMode { get; set; }
 
+    /// <summary>
+    /// Gets or sets the film-grain synthesis parameters.
+    /// </summary>
     public ObuFilmGrainParameters FilmGrainParameters { get; set; } = new ObuFilmGrainParameters();
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the reduced transform set is used.
+    /// </summary>
     public bool UseReducedTransformSet { get; set; }
 
+    /// <summary>
+    /// Gets or sets the loop-filter parameters.
+    /// </summary>
     public ObuLoopFilterParameters LoopFilterParameters { get; set; } = new ObuLoopFilterParameters();
 
+    /// <summary>
+    /// Gets or sets the loop-restoration parameters.
+    /// </summary>
     public ObuLoopRestorationParameters LoopRestorationParameters { get; set; } = new ObuLoopRestorationParameters();
 
+    /// <summary>
+    /// Gets or sets the constrained directional enhancement filter parameters.
+    /// </summary>
     public ObuConstraintDirectionalEnhancementFilterParameters CdefParameters { get; set; } = new ObuConstraintDirectionalEnhancementFilterParameters();
 
+    /// <summary>
+    /// Gets or sets the number of mode-information columns in one stored row.
+    /// </summary>
     public int ModeInfoStride { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame-end probability update is disabled.
+    /// </summary>
     public bool DisableFrameEndUpdateCdf { get; set; }
 
+    /// <summary>
+    /// Gets or sets the skip-mode parameters.
+    /// </summary>
     public ObuSkipModeParameters SkipModeParameters { get; set; } = new ObuSkipModeParameters();
 
+    /// <summary>
+    /// Gets or sets the transform-size selection mode.
+    /// </summary>
     public Av1TransformMode TransformMode { get; set; }
 
+    /// <summary>
+    /// Gets or sets the loop-filter delta parameters.
+    /// </summary>
     public ObuDeltaParameters DeltaLoopFilterParameters { get; set; } = new ObuDeltaParameters();
 
+    /// <summary>
+    /// Gets or sets the quantizer delta parameters.
+    /// </summary>
     public ObuDeltaParameters DeltaQParameters { get; set; } = new ObuDeltaParameters();
 
+    /// <summary>
+    /// Gets a value indicating whether the frame uses intra prediction only.
+    /// </summary>
     public bool IsIntra => this.FrameType is ObuFrameType.IntraOnlyFrame or ObuFrameType.KeyFrame;
 
+    /// <summary>
+    /// Gets or sets the decoded and rendered frame dimensions.
+    /// </summary>
     internal ObuFrameSize FrameSize { get; set; } = new ObuFrameSize();
 
+    /// <summary>
+    /// Gets or sets the frame width in mode-information units.
+    /// </summary>
     internal int ModeInfoColumnCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the frame height in mode-information units.
+    /// </summary>
     internal int ModeInfoRowCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether an existing reference frame is displayed without decoding a new frame.
+    /// </summary>
     internal bool ShowExistingFrame { get; set; }
 
+    /// <summary>
+    /// Gets or sets the coded frame type.
+    /// </summary>
     internal ObuFrameType FrameType { get; set; }
 
+    /// <summary>
+    /// Gets or sets the validity state of each reference-frame slot.
+    /// </summary>
     internal bool[] ReferenceValid { get; set; } = new bool[Av1Constants.ReferenceFrameCount];
 
+    /// <summary>
+    /// Gets or sets the stored order-hint state for each reference-frame slot.
+    /// </summary>
     internal bool[] ReferenceOrderHint { get; set; } = new bool[Av1Constants.ReferenceFrameCount];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the decoded frame is immediately displayed.
+    /// </summary>
     internal bool ShowFrame { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame may be displayed by a later header.
+    /// </summary>
     internal bool ShowableFrame { get; set; }
 
+    /// <summary>
+    /// Gets or sets the reference map index selected when showing an existing frame.
+    /// </summary>
     internal uint FrameToShowMapIdx { get; set; }
 
+    /// <summary>
+    /// Gets or sets the display frame identifier.
+    /// </summary>
     internal uint DisplayFrameId { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame can be decoded without state from earlier frames.
+    /// </summary>
     internal bool ErrorResilientMode { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether screen-content coding tools are permitted.
+    /// </summary>
     internal bool AllowScreenContentTools { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether probability adaptation is disabled for this frame.
+    /// </summary>
     internal bool DisableCdfUpdate { get; set; }
 
+    /// <summary>
+    /// Gets or sets the identifier of the current frame.
+    /// </summary>
     internal uint CurrentFrameId { get; set; }
 
+    /// <summary>
+    /// Gets or sets the reference-map index selected for each inter reference.
+    /// </summary>
     internal uint[] ReferenceFrameIndex { get; set; } = new uint[Av1Constants.ReferenceFrameCount];
 
+    /// <summary>
+    /// Gets or sets the frame order hint.
+    /// </summary>
     internal uint OrderHint { get; set; }
 
+    /// <summary>
+    /// Gets or sets the reference frame supplying the initial probability context.
+    /// </summary>
     internal uint PrimaryReferenceFrame { get; set; } = Av1Constants.PrimaryReferenceFrameNone;
 
+    /// <summary>
+    /// Gets or sets the bit mask of reference slots refreshed by this frame.
+    /// </summary>
     internal uint RefreshFrameFlags { get; set; }
 
-    // 5.9.31. Temporal point info syntax
+    /// <summary>
+    /// Gets or sets the presentation time signaled by temporal point information.
+    /// </summary>
     internal uint FramePresentationTime { get; set; }
 }

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

@@ -3,17 +3,38 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the coded, upscaled, and rendered dimensions of an AV1 frame.
+/// </summary>
 internal class ObuFrameSize
 {
+    /// <summary>
+    /// Gets or sets the coded frame width.
+    /// </summary>
     internal int FrameWidth { get; set; }
 
+    /// <summary>
+    /// Gets or sets the coded frame height.
+    /// </summary>
     internal int FrameHeight { get; set; }
 
+    /// <summary>
+    /// Gets or sets the denominator used by AV1 super-resolution scaling.
+    /// </summary>
     internal int SuperResolutionDenominator { get; set; }
 
+    /// <summary>
+    /// Gets or sets the frame width after super-resolution upscaling.
+    /// </summary>
     internal int SuperResolutionUpscaledWidth { get; set; }
 
+    /// <summary>
+    /// Gets or sets the intended display width.
+    /// </summary>
     internal int RenderWidth { get; set; }
 
+    /// <summary>
+    /// Gets or sets the intended display height.
+    /// </summary>
     internal int RenderHeight { get; set; }
 }

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

@@ -3,10 +3,28 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the AV1 frame type signaled by a frame header.
+/// </summary>
 internal enum ObuFrameType
 {
+    /// <summary>
+    /// A key frame that is decoded without reference to another frame.
+    /// </summary>
     KeyFrame = 0,
+
+    /// <summary>
+    /// An inter frame that can refer to previously decoded frames.
+    /// </summary>
     InterFrame = 1,
+
+    /// <summary>
+    /// An intra-only frame that does not refresh all reference slots.
+    /// </summary>
     IntraOnlyFrame = 2,
+
+    /// <summary>
+    /// A switch frame that permits switching between coded sequences.
+    /// </summary>
     SwitchFrame = 3,
 }

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

@@ -3,19 +3,43 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the parsed header and payload size of an AV1 open bitstream unit.
+/// </summary>
 internal class ObuHeader
 {
+    /// <summary>
+    /// Gets or sets the number of bytes occupied by the OBU header and its size field.
+    /// </summary>
     public int Size { get; set; }
 
+    /// <summary>
+    /// Gets or sets the OBU payload type.
+    /// </summary>
     public ObuType Type { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the OBU carries an explicit payload-size field.
+    /// </summary>
     public bool HasSize { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the OBU carries temporal and spatial identifiers.
+    /// </summary>
     public bool HasExtension { get; set; }
 
+    /// <summary>
+    /// Gets or sets the temporal-layer identifier.
+    /// </summary>
     public int TemporalId { get; set; }
 
+    /// <summary>
+    /// Gets or sets the spatial-layer identifier.
+    /// </summary>
     public int SpatialId { get; set; }
 
+    /// <summary>
+    /// Gets or sets the OBU payload size, in bytes.
+    /// </summary>
     public int PayloadSize { get; set; }
 }

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

@@ -3,27 +3,57 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the AV1 deblocking-loop-filter parameters for a frame.
+/// </summary>
 internal class ObuLoopFilterParameters
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ObuLoopFilterParameters"/> class with the AV1 default reference and mode deltas.
+    /// </summary>
     public ObuLoopFilterParameters()
     {
         this.ReferenceDeltas = [1, 0, 0, 0, 0, -1, -1, -1];
         this.ModeDeltas = [0, 0];
     }
 
+    /// <summary>
+    /// Gets or sets the horizontal and vertical luma filter levels.
+    /// </summary>
     public int[] FilterLevel { get; internal set; } = new int[2];
 
+    /// <summary>
+    /// Gets or sets the U-plane filter level.
+    /// </summary>
     public int FilterLevelU { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the V-plane filter level.
+    /// </summary>
     public int FilterLevelV { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the filter sharpness level.
+    /// </summary>
     public int SharpnessLevel { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether reference-frame and mode deltas are enabled.
+    /// </summary>
     public bool ReferenceDeltaModeEnabled { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether reference-frame and mode deltas are updated by this frame.
+    /// </summary>
     public bool ReferenceDeltaModeUpdate { get; internal set; }
 
+    /// <summary>
+    /// Gets the filter-level deltas for the AV1 reference-frame categories.
+    /// </summary>
     public int[] ReferenceDeltas { get; }
 
+    /// <summary>
+    /// Gets the filter-level deltas for the AV1 prediction modes.
+    /// </summary>
     public int[] ModeDeltas { get; }
 }

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

@@ -3,9 +3,18 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the loop-restoration type and unit size for one color plane.
+/// </summary>
 internal class ObuLoopRestorationItem
 {
+    /// <summary>
+    /// Gets or sets the restoration-unit size, in samples.
+    /// </summary>
     internal int Size { get; set; }
 
+    /// <summary>
+    /// Gets or sets the restoration filter type.
+    /// </summary>
     internal ObuRestorationType Type { get; set; } = ObuRestorationType.None;
 }

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

@@ -3,23 +3,46 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the AV1 loop-restoration configuration for a frame.
+/// </summary>
 internal class ObuLoopRestorationParameters
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ObuLoopRestorationParameters"/> class.
+    /// </summary>
     internal ObuLoopRestorationParameters()
     {
+        // AV1 addresses restoration state by plane, so all three plane entries must exist even
+        // when the active color configuration uses fewer planes.
         this.Items = new ObuLoopRestorationItem[3];
         this.Items[0] = new();
         this.Items[1] = new();
         this.Items[2] = new();
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether any plane uses loop restoration.
+    /// </summary>
     internal bool UsesLoopRestoration { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether either chroma plane uses loop restoration.
+    /// </summary>
     internal bool UsesChromaLoopRestoration { get; set; }
 
+    /// <summary>
+    /// Gets the loop-restoration configuration for each plane.
+    /// </summary>
     internal ObuLoopRestorationItem[] Items { get; }
 
+    /// <summary>
+    /// Gets or sets the luma restoration-unit size shift.
+    /// </summary>
     internal int UnitShift { get; set; }
 
+    /// <summary>
+    /// Gets or sets the chroma restoration-unit size shift relative to luma.
+    /// </summary>
     internal int UVShift { get; set; }
 }

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

@@ -3,20 +3,78 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the CICP matrix coefficients used to derive luma and chroma components.
+/// </summary>
 internal enum ObuMatrixCoefficients
 {
+    /// <summary>
+    /// The identity matrix used for GBR component ordering.
+    /// </summary>
     Identity = 0,
+
+    /// <summary>
+    /// ITU-R BT.709 coefficients.
+    /// </summary>
     Bt709 = 1,
+
+    /// <summary>
+    /// Unspecified coefficients.
+    /// </summary>
     Unspecified = 2,
+
+    /// <summary>
+    /// United States FCC 73.628 coefficients.
+    /// </summary>
     Fcc = 4,
+
+    /// <summary>
+    /// ITU-R BT.470 System B and G coefficients.
+    /// </summary>
     Bt470BG = 5,
+
+    /// <summary>
+    /// ITU-R BT.601 coefficients.
+    /// </summary>
     Bt601 = 6,
+
+    /// <summary>
+    /// SMPTE 240M coefficients.
+    /// </summary>
     Smpte240 = 7,
+
+    /// <summary>
+    /// SMPTE YCgCo coefficients.
+    /// </summary>
     SmpteYCgCo = 8,
+
+    /// <summary>
+    /// ITU-R BT.2020 non-constant-luminance coefficients.
+    /// </summary>
     Bt2020NonConstantLuminance = 9,
+
+    /// <summary>
+    /// ITU-R BT.2020 constant-luminance coefficients.
+    /// </summary>
     Bt2020ConstantLuminance = 10,
+
+    /// <summary>
+    /// SMPTE ST 2085 YDzDx coefficients.
+    /// </summary>
     Smpte2085 = 11,
+
+    /// <summary>
+    /// Chromaticity-derived non-constant-luminance coefficients.
+    /// </summary>
     ChromaticityDerivedNonConstantLuminance = 12,
-    ChromaticityDerivedConstandLuminance = 13,
+
+    /// <summary>
+    /// Chromaticity-derived constant-luminance coefficients.
+    /// </summary>
+    ChromaticityDerivedConstantLuminance = 13,
+
+    /// <summary>
+    /// ITU-R BT.2100 ICtCp coefficients.
+    /// </summary>
     Bt2100ICtCp = 14,
 }

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

@@ -3,11 +3,38 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the payload carried by an AV1 metadata OBU.
+/// </summary>
 internal enum ObuMetadataType
 {
-    ItutT35,
+    /// <summary>
-    HdrCll,
+    /// The reserved zero value.
-    HdrMdcv,
+    /// </summary>
-    Scalability,
+    Reserved = 0,
-    Timecode
+
+    /// <summary>
+    /// Content light-level metadata.
+    /// </summary>
+    HdrCll = 1,
+
+    /// <summary>
+    /// Mastering-display color-volume metadata.
+    /// </summary>
+    HdrMdcv = 2,
+
+    /// <summary>
+    /// Scalability-structure metadata.
+    /// </summary>
+    Scalability = 3,
+
+    /// <summary>
+    /// ITU-T T.35 terminal-provider metadata.
+    /// </summary>
+    ItutT35 = 4,
+
+    /// <summary>
+    /// Timecode metadata.
+    /// </summary>
+    Timecode = 5,
 }

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

@@ -3,27 +3,44 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the sequence-level constraints for an AV1 operating point.
+/// </summary>
 internal class ObuOperatingPoint
 {
+    /// <summary>
+    /// Gets or sets the operating-point index.
+    /// </summary>
     internal int OperatorIndex { get; set; }
 
+    /// <summary>
+    /// Gets or sets the AV1 sequence-level index.
+    /// </summary>
     internal int SequenceLevelIndex { get; set; }
 
+    /// <summary>
+    /// Gets or sets the sequence tier.
+    /// </summary>
     internal int SequenceTier { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether decoder-model timing is present for this operating point.
+    /// </summary>
     internal bool IsDecoderModelInfoPresent { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether an initial display delay is present for this operating point.
+    /// </summary>
     internal bool IsInitialDisplayDelayPresent { get; set; }
 
+    /// <summary>
+    /// Gets or sets the initial display delay minus one, in decoded frames.
+    /// </summary>
     internal uint InitialDisplayDelay { get; set; }
 
     /// <summary>
-    /// Gets or sets of sets the Idc bitmask. The bitmask that indicates which spatial and temporal layers should be decoded for
+    /// Gets or sets the bitmask selecting temporal and spatial layers for the operating point.
-    /// operating point i.Bit k is equal to 1 if temporal layer k should be decoded(for k between 0 and 7). Bit j+8 is equal to 1 if
+    /// A value of zero selects the complete coded sequence.
-    /// spatial layer j should be decoded(for j between 0 and 3).
-    /// However, if operating_point_idc[i] is equal to 0 then the coded video sequence has no scalability information in OBU
-    /// extension headers and the operating point applies to the entire coded video sequence.This means that all OBUs must be decoded.
-    /// It is a requirement of bitstream conformance that operating_point_idc[i] is not equal to operating_point_idc[j] for j = 0..(i- 1).
     /// </summary>
     internal uint Idc { get; set; }
 }

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

@@ -3,13 +3,28 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the sequence-level order-hint and dependent prediction-tool settings.
+/// </summary>
 internal class ObuOrderHintInfo
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether order hints are enabled.
+    /// </summary>
     public bool EnableOrderHint { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether joint compound prediction is enabled.
+    /// </summary>
     internal bool EnableJointCompound { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether reference-frame motion vectors are enabled.
+    /// </summary>
     internal bool EnableReferenceFrameMotionVectors { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of bits used to encode order hints.
+    /// </summary>
     internal int OrderHintBits { get; set; }
 }

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

@@ -3,19 +3,43 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the AV1 quantization parameters for a frame.
+/// </summary>
 internal class ObuQuantizationParameters
 {
+    /// <summary>
+    /// Gets or sets the base quantizer index.
+    /// </summary>
     public int BaseQIndex { get; set; }
 
+    /// <summary>
+    /// Gets or sets the effective quantizer index for each segment.
+    /// </summary>
     public int[] QIndex { get; set; } = new int[Av1Constants.MaxSegmentCount];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether quantization matrices are enabled.
+    /// </summary>
     public bool IsUsingQMatrix { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the DC quantizer-index deltas for the Y, U, and V planes.
+    /// </summary>
     public int[] DeltaQDc { get; internal set; } = new int[3];
 
+    /// <summary>
+    /// Gets or sets the AC quantizer-index deltas for the Y, U, and V planes.
+    /// </summary>
     public int[] DeltaQAc { get; internal set; } = new int[3];
 
+    /// <summary>
+    /// Gets or sets the quantization-matrix level for the Y, U, and V planes.
+    /// </summary>
     public int[] QMatrix { get; internal set; } = new int[3];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the U and V planes use separate quantizer deltas.
+    /// </summary>
     public bool HasSeparateUvDelta { get; internal set; }
 }

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

@@ -3,8 +3,18 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies whether inter blocks use only single references or can select compound references.
+/// </summary>
 internal enum ObuReferenceMode
 {
-    ReferenceModeSelect,
+    /// <summary>
-    SingleReference,
+    /// Only single-reference prediction is permitted.
+    /// </summary>
+    SingleReference = 0,
+
+    /// <summary>
+    /// Each eligible block selects single- or compound-reference prediction.
+    /// </summary>
+    ReferenceModeSelect = 1,
 }

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

@@ -3,10 +3,28 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the loop-restoration mode encoded by the two-bit frame-restoration syntax.
+/// </summary>
 internal enum ObuRestorationType : uint
 {
+    /// <summary>
+    /// Loop restoration is disabled.
+    /// </summary>
     None = 0,
+
+    /// <summary>
+    /// Each restoration unit selects its filter type.
+    /// </summary>
     Switchable = 1,
-    Weiner = 2,
+
+    /// <summary>
+    /// Separable Wiener filtering is used.
+    /// </summary>
+    Wiener = 2,
+
+    /// <summary>
+    /// Self-guided restoration projection is used.
+    /// </summary>
     SgrProj = 3,
 }

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

@@ -3,14 +3,48 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies a feature that AV1 can configure independently for each segment.
+/// </summary>
 internal enum ObuSegmentationLevelFeature
 {
+    /// <summary>
+    /// Adjusts the segment quantizer index.
+    /// </summary>
     AlternativeQuantizer,
+
+    /// <summary>
+    /// Adjusts the vertical luma loop-filter level.
+    /// </summary>
     AlternativeLoopFilterYVertical,
+
+    /// <summary>
+    /// Adjusts the horizontal luma loop-filter level.
+    /// </summary>
     AlternativeLoopFilterYHorizontal,
+
+    /// <summary>
+    /// Adjusts the U-plane loop-filter level.
+    /// </summary>
     AlternativeLoopFilterU,
+
+    /// <summary>
+    /// Adjusts the V-plane loop-filter level.
+    /// </summary>
     AlternativeLoopFilterV,
+
+    /// <summary>
+    /// Selects a reference frame for the segment.
+    /// </summary>
     ReferenceFrame,
+
+    /// <summary>
+    /// Marks every block in the segment as skipped.
+    /// </summary>
     Skip,
+
+    /// <summary>
+    /// Uses the global motion vector for the segment.
+    /// </summary>
     GlobalMotionVector,
 }

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

@@ -3,39 +3,62 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the AV1 segmentation state and per-segment feature values for a frame.
+/// </summary>
 internal class ObuSegmentationParameters
 {
+    /// <summary>
+    /// Gets or sets the effective quantization-matrix level for each plane and segment.
+    /// </summary>
     public int[][] QMLevel { get; internal set; } = new int[3][];
 
+    /// <summary>
+    /// Gets or sets the enabled state of every feature for every segment.
+    /// </summary>
     public bool[,] FeatureEnabled { get; internal set; } = new bool[Av1Constants.MaxSegmentCount, Av1Constants.SegmentationLevelMax];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether segmentation is enabled for the frame.
+    /// </summary>
     public bool Enabled { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the value of every feature for every segment.
+    /// </summary>
     public int[,] FeatureData { get; internal set; } = new int[Av1Constants.MaxSegmentCount, Av1Constants.SegmentationLevelMax];
 
+    /// <summary>
+    /// Gets or sets a value indicating whether segment identifiers are decoded before skip-mode decisions.
+    /// </summary>
     public bool SegmentIdPrecedesSkip { get; internal set; }
 
+    /// <summary>
+    /// Gets or sets the greatest segment identifier that has at least one active feature.
+    /// </summary>
     public int LastActiveSegmentId { get; internal set; }
 
     /// <summary>
-    /// Gets or sets the SegmentationUpdateMap. A value of 1 indicates that the segmentation map are updated during the decoding of this
+    /// Gets or sets a value indicating whether the segmentation map is updated while decoding the frame.
-    /// frame. SegmentationUpdateMap equal to 0 means that the segmentation map from the previous frame is used.
     /// </summary>
     public int SegmentationUpdateMap { get; internal set; }
 
     /// <summary>
-    /// Gets or sets the SegmentationTemporalUpdate. A value of 1 indicates that the updates to the segmentation map are coded relative to the
+    /// Gets or sets a value indicating whether segmentation-map updates are coded relative to the existing map.
-    /// existing segmentation map. SegmentationTemporalUpdate equal to 0 indicates that the new segmentation map is coded
-    /// without reference to the existing segmentation map.
     /// </summary>
     public int SegmentationTemporalUpdate { get; internal set; }
 
     /// <summary>
-    /// Gets or sets SegmentationUpdateData. A value of 1 indicates that new parameters are about to be specified for each segment.
+    /// Gets or sets a value indicating whether the frame supplies new per-segment feature data.
-    /// SegmentationUpdateData equal to 0 indicates that the segmentation parameters should keep their existing values.
     /// </summary>
     public int SegmentationUpdateData { get; internal set; }
 
+    /// <summary>
+    /// Determines whether a feature is active for a segment.
+    /// </summary>
+    /// <param name="segmentId">The segment identifier.</param>
+    /// <param name="feature">The feature to inspect.</param>
+    /// <returns><see langword="true"/> when the feature is active; otherwise, <see langword="false"/>.</returns>
     internal bool IsFeatureActive(int segmentId, ObuSegmentationLevelFeature feature)
         => this.FeatureEnabled[segmentId, (int)feature];
 }

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

@@ -3,93 +3,215 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Stores AV1 sequence capabilities, dimensions, timing, and color configuration.
+/// </summary>
 internal class ObuSequenceHeader
 {
+    /// <summary>
+    /// Backs <see cref="Use128x128Superblock"/> while its dependent geometry is updated.
+    /// </summary>
     private bool use128x128Superblock;
 
+    /// <summary>
+    /// Gets or sets a value indicating whether filter-intra prediction is enabled.
+    /// </summary>
     public bool EnableFilterIntra { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether constrained directional enhancement filtering is enabled.
+    /// </summary>
     public bool EnableCdef { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the sequence contains one still picture.
+    /// </summary>
     public bool IsStillPicture { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the reduced still-picture header syntax is used.
+    /// </summary>
     public bool IsReducedStillPictureHeader { get; set; }
 
+    /// <summary>
+    /// Gets or sets the sequence profile.
+    /// </summary>
     public ObuSequenceProfile SequenceProfile { get; set; }
 
+    /// <summary>
+    /// Gets or sets the signaled operating points.
+    /// </summary>
     public ObuOperatingPoint[] OperatingPoint { get; set; } = new ObuOperatingPoint[1];
 
+    /// <summary>
+    /// Gets or sets the decoder-buffer model information when present.
+    /// </summary>
     public ObuDecoderModelInfo? DecoderModelInfo { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether operating points may carry initial display delays.
+    /// </summary>
     public bool InitialDisplayDelayPresentFlag { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether decoder-model information is present.
+    /// </summary>
     public bool DecoderModelInfoPresentFlag { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether sequence timing information is present.
+    /// </summary>
     public bool TimingInfoPresentFlag { get; set; }
 
+    /// <summary>
+    /// Gets or sets the sequence timing information when present.
+    /// </summary>
     public ObuTimingInfo? TimingInfo { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether frame identifiers are signaled.
+    /// </summary>
     public bool IsFrameIdNumbersPresent { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of bits used to signal frame widths minus one.
+    /// </summary>
     public int FrameWidthBits { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of bits used to signal frame heights minus one.
+    /// </summary>
     public int FrameHeightBits { get; set; }
 
+    /// <summary>
+    /// Gets or sets the maximum decoded frame width in pixels.
+    /// </summary>
     public int MaxFrameWidth { get; set; }
 
+    /// <summary>
+    /// Gets or sets the maximum decoded frame height in pixels.
+    /// </summary>
     public int MaxFrameHeight { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether 128x128 superblocks are used.
+    /// </summary>
     public bool Use128x128Superblock
     {
         get => this.use128x128Superblock;
         set
         {
             this.use128x128Superblock = value;
+
+            // Superblock selection controls every downstream partition-grid unit, so update the derived geometry atomically.
             this.SuperblockSize = value ? Av1BlockSize.Block128x128 : Av1BlockSize.Block64x64;
             this.SuperblockSizeLog2 = value ? 7 : 6;
             this.SuperblockModeInfoSize = 1 << (this.SuperblockSizeLog2 - Av1Constants.ModeInfoSizeLog2);
         }
     }
 
+    /// <summary>
+    /// Gets the selected superblock dimensions.
+    /// </summary>
     public Av1BlockSize SuperblockSize { get; private set; }
 
+    /// <summary>
+    /// Gets the superblock width and height in mode-information units.
+    /// </summary>
     public int SuperblockModeInfoSize { get; private set; }
 
+    /// <summary>
+    /// Gets the base-two logarithm of the superblock size in pixels.
+    /// </summary>
     public int SuperblockSizeLog2 { get; private set; }
 
+    /// <summary>
+    /// Gets or sets the filter-intra capability level.
+    /// </summary>
     public int FilterIntraLevel { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether intra edge filtering is enabled.
+    /// </summary>
     public bool EnableIntraEdgeFilter { get; set; }
 
+    /// <summary>
+    /// Gets or sets the order-hint capabilities.
+    /// </summary>
     public ObuOrderHintInfo OrderHintInfo { get; set; } = new ObuOrderHintInfo();
 
+    /// <summary>
+    /// Gets or sets a value indicating whether order hints are enabled.
+    /// </summary>
     public bool EnableOrderHint { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether inter-intra compound prediction is enabled.
+    /// </summary>
     public bool EnableInterIntraCompound { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether masked compound prediction is enabled.
+    /// </summary>
     public bool EnableMaskedCompound { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether warped motion is enabled.
+    /// </summary>
     public bool EnableWarpedMotion { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether independent horizontal and vertical interpolation filters are enabled.
+    /// </summary>
     public bool EnableDualFilter { get; set; }
 
+    /// <summary>
+    /// Gets or sets the sequence-level integer-motion-vector selection.
+    /// </summary>
     public int ForceIntegerMotionVector { get; set; }
 
+    /// <summary>
+    /// Gets or sets the sequence-level screen-content-tools selection.
+    /// </summary>
     public int ForceScreenContentTools { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether frame super-resolution is enabled.
+    /// </summary>
     public bool EnableSuperResolution { get; set; }
 
+    /// <summary>
+    /// Gets or sets the constrained directional enhancement filter capability level.
+    /// </summary>
     public int CdefLevel { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether loop restoration is enabled.
+    /// </summary>
     public bool EnableRestoration { get; set; }
 
+    /// <summary>
+    /// Gets or sets the decoded color configuration.
+    /// </summary>
     public ObuColorConfig ColorConfig { get; set; } = new ObuColorConfig();
 
+    /// <summary>
+    /// Gets or sets a value indicating whether frame headers may carry film-grain parameters.
+    /// </summary>
     public bool AreFilmGrainingParametersPresent { get; set; }
 
+    /// <summary>
+    /// Gets or sets the total number of bits in a frame identifier.
+    /// </summary>
     public int FrameIdLength { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of bits in a delta frame identifier.
+    /// </summary>
     public int DeltaFrameIdLength { get; set; }
 
+    /// <summary>
+    /// Gets or sets the additional frame-identifier bit count signaled by the sequence header.
+    /// </summary>
     public uint AdditionalFrameIdLength { get; set; }
 }

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

@@ -3,9 +3,23 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the AV1 sequence profile and its permitted bit-depth and chroma formats.
+/// </summary>
 internal enum ObuSequenceProfile : uint
 {
+    /// <summary>
+    /// The Main profile.
+    /// </summary>
     Main = 0,
+
+    /// <summary>
+    /// The High profile.
+    /// </summary>
     High = 1,
+
+    /// <summary>
+    /// The Professional profile.
+    /// </summary>
     Professional = 2,
 }

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

@@ -3,9 +3,18 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the availability and enabled state of AV1 skip mode for a frame.
+/// </summary>
 internal class ObuSkipModeParameters
 {
+    /// <summary>
+    /// Gets or sets a value indicating whether the frame is permitted to use skip mode.
+    /// </summary>
     public bool SkipModeAllowed { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether skip mode is enabled for the frame.
+    /// </summary>
     public bool SkipModeFlag { get; internal set; }
 }

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

@@ -3,37 +3,88 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the tile layout derived from an AV1 frame header.
+/// </summary>
 internal class ObuTileGroupHeader
 {
+    /// <summary>
+    /// Gets or sets the maximum tile width, in superblocks.
+    /// </summary>
     internal int MaxTileWidthSuperblock { get; set; }
 
+    /// <summary>
+    /// Gets or sets the maximum tile height, in superblocks.
+    /// </summary>
     internal int MaxTileHeightSuperblock { get; set; }
 
+    /// <summary>
+    /// Gets or sets the minimum base-2 logarithm of the tile-column count.
+    /// </summary>
     internal int MinLog2TileColumnCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the maximum base-2 logarithm of the tile-column count.
+    /// </summary>
     internal int MaxLog2TileColumnCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the maximum base-2 logarithm of the tile-row count.
+    /// </summary>
     internal int MaxLog2TileRowCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the minimum base-2 logarithm of the total tile count.
+    /// </summary>
     internal int MinLog2TileCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether tile columns and rows use uniform spacing.
+    /// </summary>
     public bool HasUniformTileSpacing { get; set; }
 
+    /// <summary>
+    /// Gets or sets the base-2 logarithm of the tile-column count.
+    /// </summary>
     internal int TileColumnCountLog2 { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of tile columns.
+    /// </summary>
     internal int TileColumnCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the starting superblock column for each tile column.
+    /// </summary>
     internal int[] TileColumnStartModeInfo { get; set; } = new int[Av1Constants.MaxTileRowCount + 1];
 
+    /// <summary>
+    /// Gets or sets the minimum base-2 logarithm of the tile-row count.
+    /// </summary>
     internal int MinLog2TileRowCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the base-2 logarithm of the tile-row count.
+    /// </summary>
     internal int TileRowCountLog2 { get; set; }
 
+    /// <summary>
+    /// Gets or sets the starting superblock row for each tile row.
+    /// </summary>
     internal int[] TileRowStartModeInfo { get; set; } = new int[Av1Constants.MaxTileColumnCount + 1];
 
+    /// <summary>
+    /// Gets or sets the number of tile rows.
+    /// </summary>
     internal int TileRowCount { get; set; }
 
+    /// <summary>
+    /// Gets or sets the tile whose entropy context is retained after frame decoding.
+    /// </summary>
     internal uint ContextUpdateTileId { get; set; }
 
+    /// <summary>
+    /// Gets or sets the number of bytes used to signal each tile size.
+    /// </summary>
     internal int TileSizeBytes { get; set; }
 }

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

@@ -3,6 +3,9 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Contains the timing syntax signaled by an AV1 sequence header.
+/// </summary>
 internal class ObuTimingInfo
 {
     /// <summary>

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

@@ -3,23 +3,93 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies the CICP transfer characteristics signaled by an AV1 sequence.
+/// </summary>
 internal enum ObuTransferCharacteristics
 {
+    /// <summary>
+    /// ITU-R BT.709 transfer characteristics.
+    /// </summary>
     Bt709 = 1,
+
+    /// <summary>
+    /// Unspecified transfer characteristics.
+    /// </summary>
     Unspecified = 2,
+
+    /// <summary>
+    /// ITU-R BT.470 System M transfer characteristics.
+    /// </summary>
     Bt470M = 4,
+
+    /// <summary>
+    /// ITU-R BT.470 System B and G transfer characteristics.
+    /// </summary>
     Bt470BG = 5,
+
+    /// <summary>
+    /// ITU-R BT.601 transfer characteristics.
+    /// </summary>
     Bt601 = 6,
+
+    /// <summary>
+    /// SMPTE 240M transfer characteristics.
+    /// </summary>
     Smpte240 = 7,
+
+    /// <summary>
+    /// Linear light.
+    /// </summary>
     Linear = 8,
+
+    /// <summary>
+    /// Logarithmic transfer with a 100:1 range.
+    /// </summary>
     Log100 = 9,
+
+    /// <summary>
+    /// Logarithmic transfer with a 100 times square-root-of-ten to one range.
+    /// </summary>
     Log100Sqrt10 = 10,
+
+    /// <summary>
+    /// IEC 61966-2-4 transfer characteristics.
+    /// </summary>
     Iec61966 = 11,
+
+    /// <summary>
+    /// ITU-R BT.1361 transfer characteristics.
+    /// </summary>
     Bt1361 = 12,
+
+    /// <summary>
+    /// IEC 61966-2-1 sRGB or sYCC transfer characteristics.
+    /// </summary>
     Srgb = 13,
+
+    /// <summary>
+    /// ITU-R BT.2020 transfer characteristics for 10-bit systems.
+    /// </summary>
     Bt202010Bit = 14,
+
+    /// <summary>
+    /// ITU-R BT.2020 transfer characteristics for 12-bit systems.
+    /// </summary>
     Bt202012Bit = 15,
+
+    /// <summary>
+    /// SMPTE ST 2084 perceptual-quantizer transfer characteristics.
+    /// </summary>
     Smpte2084 = 16,
-    Smpte248 = 17,
+
+    /// <summary>
+    /// SMPTE ST 428 transfer characteristics.
+    /// </summary>
+    Smpte428 = 17,
+
+    /// <summary>
+    /// ITU-R BT.2100 hybrid-log-gamma transfer characteristics.
+    /// </summary>
     Hlg = 18,
 }

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

@@ -3,16 +3,58 @@
 
 namespace SixLabors.ImageSharp.Formats.Heif.Av1.OpenBitstreamUnit;
 
+/// <summary>
+/// Identifies an AV1 open bitstream unit payload.
+/// </summary>
 internal enum ObuType
 {
+    /// <summary>
+    /// The reserved zero value.
+    /// </summary>
     None = 0,
+
+    /// <summary>
+    /// A sequence header.
+    /// </summary>
     SequenceHeader = 1,
+
+    /// <summary>
+    /// A temporal delimiter.
+    /// </summary>
     TemporalDelimiter = 2,
+
+    /// <summary>
+    /// A frame header without tile data.
+    /// </summary>
     FrameHeader = 3,
-    RedundantFrameHeader = 7,
+
+    /// <summary>
+    /// One or more encoded tiles.
+    /// </summary>
     TileGroup = 4,
+
+    /// <summary>
+    /// Metadata associated with the coded sequence.
+    /// </summary>
     Metadata = 5,
+
+    /// <summary>
+    /// A frame header followed by tile data.
+    /// </summary>
     Frame = 6,
+
+    /// <summary>
+    /// A repeated copy of the current frame header.
+    /// </summary>
+    RedundantFrameHeader = 7,
+
+    /// <summary>
+    /// A list of tiles for large-scale tile decoding.
+    /// </summary>
     TileList = 8,
+
+    /// <summary>
+    /// Padding bytes.
+    /// </summary>
     Padding = 15,
 }