C# 使用 FFmpeg.dll 进行图片 H264 编码

首先，需要安装 FFmpeg，可以从其官网下载。然后，需要将 FFmpeg 的库文件 (libavcodec、libavformat、libavutil、libswscale) 与 FFmpeg 的头文件 (avcodec.h、avformat.h、avutil.h、swscale.h) 添加到 C# 项目中。

接下来，可以使用 FFmpeg 的 C# 封装库 FFmpeg.AutoGen，该库提供了与 FFmpeg 库交互的类和方法。在使用之前，需要通过 FFmpeg 的头文件生成 C# 代码，可以使用 T4FFmpeg 库完成这个过程。

以下是使用 FFmpeg.dll 进行图片 h264 编码的示例代码：

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using FFmpeg.AutoGen;

namespace ImageEncoding
{
    class Program
    {
        static void Main(string[] args)
        {
            // Initialize FFmpeg
            FFmpegBinariesHelper.RegisterFFmpegBinaries();

            // Input image path
            string imagePath = 'input.png';

            // Output video path
            string videoPath = 'output.mp4';

            // Initialize input image
            Bitmap inputImage = new Bitmap(imagePath);

            // Initialize output video codec
            AVCodecID codecId = AVCodecID.AV_CODEC_ID_H264;
            AVCodec codec = ffmpeg.avcodec_find_encoder(codecId);
            if (codec == null)
            {
                throw new InvalidOperationException('Codec not found.');
            }

            // Initialize output video codec context
            AVCodecContext codecContext = ffmpeg.avcodec_alloc_context3(codec);
            codecContext.width = inputImage.Width;
            codecContext.height = inputImage.Height;
            codecContext.pix_fmt = AVPixelFormat.AV_PIX_FMT_YUV420P;
            codecContext.time_base = new AVRational { num = 1, den = 25 };
            codecContext.max_b_frames = 2;
            codecContext.bit_rate = 400000;
            codecContext.gop_size = 10;
            codecContext.flags |= ffmpeg.AV_CODEC_FLAG_GLOBAL_HEADER;

            // Open output video codec
            ffmpeg.avcodec_open2(codecContext, codec, null).ThrowOnError();

            // Initialize output video frame
            AVFrame outputFrame = ffmpeg.av_frame_alloc();
            outputFrame.width = inputImage.Width;
            outputFrame.height = inputImage.Height;
            outputFrame.format = (int)codecContext.pix_fmt;
            ffmpeg.av_frame_get_buffer(outputFrame, 32).ThrowOnError();

            // Initialize input video packet
            AVPacket inputPacket = new AVPacket();
            ffmpeg.av_init_packet(ref inputPacket);
            inputPacket.data = IntPtr.Zero;
            inputPacket.size = 0;

            // Initialize output video packet
            AVPacket outputPacket = new AVPacket();
            ffmpeg.av_init_packet(ref outputPacket);
            outputPacket.data = IntPtr.Zero;
            outputPacket.size = 0;

            // Initialize output video format context
            AVFormatContext outputFormatContext = ffmpeg.avformat_alloc_context();
            outputFormatContext.oformat = ffmpeg.av_guess_format(null, videoPath, null);
            outputFormatContext.video_codec = codec;

            // Open output video format
            ffmpeg.avio_open(out outputFormatContext.pb, videoPath, ffmpeg.AVIO_FLAG_WRITE).ThrowOnError();

            // Initialize output video stream
            AVStream outputStream = ffmpeg.avformat_new_stream(outputFormatContext, codec);
            ffmpeg.avcodec_parameters_from_context(outputStream.codecpar, codecContext);

            // Write output video header
            ffmpeg.avformat_write_header(outputFormatContext, null).ThrowOnError();

            // Initialize input image data
            byte[] inputData = new byte[inputImage.Width * inputImage.Height * 3];
            int inputIndex = 0;
            for (int y = 0; y < inputImage.Height; y++)
            {
                for (int x = 0; x < inputImage.Width; x++)
                {
                    Color color = inputImage.GetPixel(x, y);
                    inputData[inputIndex++] = color.R;
                    inputData[inputIndex++] = color.G;
                    inputData[inputIndex++] = color.B;
                }
            }

            // Set input image data to output video frame
            AVFrame inputFrame = ffmpeg.av_frame_alloc();
            inputFrame.width = inputImage.Width;
            inputFrame.height = inputImage.Height;
            inputFrame.format = (int)AVPixelFormat.AV_PIX_FMT_RGB24;
            ffmpeg.av_frame_get_buffer(inputFrame, 32).ThrowOnError();
            ffmpeg.av_image_fill_arrays(inputFrame.data, inputFrame.linesize, inputData, AVPixelFormat.AV_PIX_FMT_RGB24, inputImage.Width, inputImage.Height, 1);

            // Encode input video frame and write to output video stream
            ffmpeg.avcodec_send_frame(codecContext, inputFrame).ThrowOnError();
            while (true)
            {
                int result = ffmpeg.avcodec_receive_packet(codecContext, ref outputPacket);
                if (result == ffmpeg.AVERROR(ffmpeg.EAGAIN) || result == ffmpeg.AVERROR_EOF)
                {
                    break;
                }
                outputPacket.stream_index = outputStream.index;
                ffmpeg.av_packet_rescale_ts(ref outputPacket, codecContext.time_base, outputStream.time_base);
                ffmpeg.av_interleaved_write_frame(outputFormatContext, ref outputPacket).ThrowOnError();
                ffmpeg.av_packet_unref(ref outputPacket);
            }

            // Write output video trailer
            ffmpeg.av_write_trailer(outputFormatContext).ThrowOnError();

            // Free resources
            ffmpeg.av_packet_unref(ref inputPacket);
            ffmpeg.av_packet_unref(ref outputPacket);
            ffmpeg.av_frame_unref(inputFrame);
            ffmpeg.av_frame_free(ref inputFrame);
            ffmpeg.av_frame_unref(outputFrame);
            ffmpeg.av_frame_free(ref outputFrame);
            ffmpeg.avcodec_close(codecContext);
            ffmpeg.avcodec_free_context(ref codecContext);
            ffmpeg.avio_close(outputFormatContext.pb);
            ffmpeg.avformat_free_context(outputFormatContext);
        }
    }
}

这段代码将输入的图片转换为 YUV420P 格式的视频，并将其编码为 H.264 格式。可以通过调整编码参数来控制输出视频的质量和大小。