The following code is a class for creating, opening, or editing a Gif.
He cannot read the playback time from the stream, but for the second part of your question, he can write a Gif animation with the specified delay on each frame.
using System; using System.Collections; using System.Collections.Generic; using System.Drawing; using System.Drawing.Imaging; using System.IO; /// <summary> /// Uses default .net GIF encoding and adds animation headers. /// </summary> public class Gif : IDisposable, IEnumerable<Image> { #region Header Constants const byte FileTrailer = 0x3b, ApplicationBlockSize = 0x0b, GraphicControlExtensionBlockSize = 0x04; const int ApplicationExtensionBlockIdentifier = 0xff21, GraphicControlExtensionBlockIdentifier = 0xf921; const long SourceGlobalColorInfoPosition = 10, SourceGraphicControlExtensionPosition = 781, SourceGraphicControlExtensionLength = 8, SourceImageBlockPosition = 789, SourceImageBlockHeaderLength = 11, SourceColorBlockPosition = 13, SourceColorBlockLength = 768; const string ApplicationIdentification = "NETSCAPE2.0", FileType = "GIF", FileVersion = "89a"; #endregion class GifFrame { public GifFrame(Image image, double delay, int xOffset, int yOffset) { Image = image; Delay = delay; XOffset = xOffset; YOffset = yOffset; } public Image Image; public double Delay; public int XOffset, YOffset; } List<GifFrame> Frames = new List<GifFrame>(); public Gif() { DefaultFrameDelay = 500; } public Gif(Stream InStream, int Repeat = 0, int Delay = 500) { using (Image Animation = Bitmap.FromStream(InStream)) { int Length = Animation.GetFrameCount(FrameDimension.Time); DefaultFrameDelay = Delay; this.Repeat = Repeat; for (int i = 0; i < Length; ++i) { Animation.SelectActiveFrame(FrameDimension.Time, i); var Frame = new Bitmap(Animation.Size.Width, Animation.Size.Height); Graphics.FromImage(Frame).DrawImage(Animation, new Point(0, 0)); Frames.Add(new GifFrame(Frame, Delay, 0, 0)); } } } #region Properties public int DefaultWidth { get; set; } public int DefaultHeight { get; set; } public int Count { get { return Frames.Count; } } /// <summary> /// Default Delay in Milliseconds /// </summary> public int DefaultFrameDelay { get; set; } public int Repeat { get; private set; } #endregion /// <summary> /// Adds a frame to this animation. /// </summary> /// <param name="Image">The image to add</param> /// <param name="XOffset">The positioning x offset this image should be displayed at.</param> /// <param name="YOffset">The positioning y offset this image should be displayed at.</param> public void AddFrame(Image Image, double? frameDelay = null, int XOffset = 0, int YOffset = 0) { Frames.Add(new GifFrame(Image, frameDelay ?? DefaultFrameDelay, XOffset, YOffset)); } public void AddFrame(string FilePath, double? frameDelay = null, int XOffset = 0, int YOffset = 0) { AddFrame(new Bitmap(FilePath), frameDelay, XOffset, YOffset); } public void RemoveAt(int Index) { Frames.RemoveAt(Index); } public void Clear() { Frames.Clear(); } public void Save(Stream OutStream) { using (var Writer = new BinaryWriter(OutStream)) { for (int i = 0; i < Count; ++i) { var Frame = Frames[i]; using (var gifStream = new MemoryStream()) { Frame.Image.Save(gifStream, ImageFormat.Gif); // Steal the global color table info if (i == 0) InitHeader(gifStream, Writer, Frame.Image.Width, Frame.Image.Height); WriteGraphicControlBlock(gifStream, Writer, Frame.Delay); WriteImageBlock(gifStream, Writer, i != 0, Frame.XOffset, Frame.YOffset, Frame.Image.Width, Frame.Image.Height); } } // Complete File Writer.Write(FileTrailer); } } #region Write void InitHeader(Stream sourceGif, BinaryWriter Writer, int w, int h) { // File Header Writer.Write(FileType.ToCharArray()); Writer.Write(FileVersion.ToCharArray()); Writer.Write((short)(DefaultWidth == 0 ? w : DefaultWidth)); // Initial Logical Width Writer.Write((short)(DefaultHeight == 0 ? h : DefaultHeight)); // Initial Logical Height sourceGif.Position = SourceGlobalColorInfoPosition; Writer.Write((byte)sourceGif.ReadByte()); // Global Color Table Info Writer.Write((byte)0); // Background Color Index Writer.Write((byte)0); // Pixel aspect ratio WriteColorTable(sourceGif, Writer); // App Extension Header unchecked { Writer.Write((short)ApplicationExtensionBlockIdentifier); }; Writer.Write((byte)ApplicationBlockSize); Writer.Write(ApplicationIdentification.ToCharArray()); Writer.Write((byte)3); // Application block length Writer.Write((byte)1); Writer.Write((short)Repeat); // Repeat count for images. Writer.Write((byte)0); // terminator } void WriteColorTable(Stream sourceGif, BinaryWriter Writer) { sourceGif.Position = SourceColorBlockPosition; // Locating the image color table var colorTable = new byte[SourceColorBlockLength]; sourceGif.Read(colorTable, 0, colorTable.Length); Writer.Write(colorTable, 0, colorTable.Length); } void WriteGraphicControlBlock(Stream sourceGif, BinaryWriter Writer, double frameDelay) { sourceGif.Position = SourceGraphicControlExtensionPosition; // Locating the source GCE var blockhead = new byte[SourceGraphicControlExtensionLength]; sourceGif.Read(blockhead, 0, blockhead.Length); // Reading source GCE unchecked { Writer.Write((short)GraphicControlExtensionBlockIdentifier); }; // Identifier Writer.Write((byte)GraphicControlExtensionBlockSize); // Block Size Writer.Write((byte)(blockhead[3] & 0xf7 | 0x08)); // Setting disposal flag Writer.Write((short)(frameDelay / 10)); // Setting frame delay Writer.Write((byte)blockhead[6]); // Transparent color index Writer.Write((byte)0); // Terminator } void WriteImageBlock(Stream sourceGif, BinaryWriter Writer, bool includeColorTable, int x, int y, int w, int h) { sourceGif.Position = SourceImageBlockPosition; // Locating the image block var header = new byte[SourceImageBlockHeaderLength]; sourceGif.Read(header, 0, header.Length); Writer.Write((byte)header[0]); // Separator Writer.Write((short)x); // Position X Writer.Write((short)y); // Position Y Writer.Write((short)w); // Width Writer.Write((short)h); // Height if (includeColorTable) // If first frame, use global color table - else use local { sourceGif.Position = SourceGlobalColorInfoPosition; Writer.Write((byte)(sourceGif.ReadByte() & 0x3f | 0x80)); // Enabling local color table WriteColorTable(sourceGif, Writer); } else Writer.Write((byte)(header[9] & 0x07 | 0x07)); // Disabling local color table Writer.Write((byte)header[10]); // LZW Min Code Size // Read/Write image data sourceGif.Position = SourceImageBlockPosition + SourceImageBlockHeaderLength; var dataLength = sourceGif.ReadByte(); while (dataLength > 0) { var imgData = new byte[dataLength]; sourceGif.Read(imgData, 0, dataLength); Writer.Write((byte)dataLength); Writer.Write(imgData, 0, dataLength); dataLength = sourceGif.ReadByte(); } Writer.Write((byte)0); // Terminator }