在以下代码段中，您可以看到如何计算总持续时间，即累加每一帧的持续时间：
for (int f = 0; f < frameCount; f++)
{
this_delay = BitConverter.ToInt32(image.GetPropertyItem(20736).Value, index) * 10;
// Minimum delay is 100 ms
delay += (this_delay < 100 ? 100 : this_delay);
index += 4;
}
请注意，帧持续时间不能短于 100 毫秒，这可能会导致您的计算差异。
您可以阅读这篇关于检查 .GIF 的帖子，您可以在其中找到其余代码。
此外，要编辑动画图像的最后一帧，您可以使用
gifImage.SelectActiveFrame(dimension, first_frame_index);
SelectActiveFrame将允许您编辑图像，更改指定的（在您的情况下为第一个）帧。
我对此并不完全确定，但该框架不支持添加帧，为此我使用MagickNet重新编码了一个新的 GIF。您可能还想看看NGif作为替代方案。
下面的代码是一个用于创建、打开或编辑 Gif 的类。
它无法从流中读取播放时间，但对于您问题的第二部分，它可以在每帧上编写具有指定延迟的 Gif 动画。
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
}
#endregion
public void Dispose()
{
Frames.Clear();
Frames = null;
}
public Image this[int Index] { get { return Frames[Index].Image; } }
public IEnumerator<Image> GetEnumerator() { foreach (var Frame in Frames) yield return Frame.Image; }
IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); }
}