CloudMusic/FNZCM2/FNZCM2.Abstractions/Utility/FfMpegReader.cs

using System.Runtime.InteropServices;
using System.Text;
using FFmpeg.AutoGen;
using FNZCM2.Abstractions.Models.Metadata;

namespace FNZCM2.Abstractions.Utility;

//有ChatGPT参与辅助生成

public static class FfMpegReader
{
    static FfMpegReader()
    {
        ffmpeg.RootPath = "./libFFMPEG/bin";
    }

    public static unsafe FfMpegReadResult? Read(string filePath, out string? err)
    {
        // 创建 AVFormatContext 对象
        var formatContext = ffmpeg.avformat_alloc_context();
        try
        {
            var avFormatOpenInputRet = ffmpeg.avformat_open_input(&formatContext, filePath, null, null);
            if (avFormatOpenInputRet != 0)
            {
                var buf = stackalloc byte[512];
                ffmpeg.av_strerror(avFormatOpenInputRet, buf, 512);
                var str = Encoding.ASCII.GetString(buf, 512).TrimEnd('\0');
                err = "open:" + str;
                return null;
            }

            // 读取流信息
            if (ffmpeg.avformat_find_stream_info(formatContext, null) != 0)
            {
                var buf = stackalloc byte[512];
                ffmpeg.av_strerror(avFormatOpenInputRet, buf, 512);
                var str = Encoding.ASCII.GetString(buf, 512).TrimEnd('\0');
                err = "find stream:" + str;
                return null;
            }

            int? durMs = formatContext->duration > 0 ? (int)(formatContext->duration / 1000) : null;
            int? bitRate = formatContext->bit_rate > 0 ? (int)formatContext->bit_rate : null;

            // 初始化流列表
            List<FfMpegReadResult.MediaStream> streams = new();

            // 遍历流信息
            for (var i = 0; i < formatContext->nb_streams; i++)
            {
                var stream = formatContext->streams[i];

                var codecParams = stream->codecpar;
                var codecType = codecParams->codec_type;

                // 准备局部变量
                var type = codecType;
                var codec = codecParams->codec_id;

                AudioInfo? audioInfo = null;
                PictureInfo? pictureInfo = null;

                // 处理音频流
                if (codecType == AVMediaType.AVMEDIA_TYPE_AUDIO)
                {
                    var sampleFormat = (AVSampleFormat)codecParams->format;

                    int? bitPerSample = codecParams->bits_per_raw_sample;
                    int? sampleRate = codecParams->sample_rate;

                    bitPerSample = bitPerSample <= 0 ? null : bitPerSample;
                    sampleRate = sampleRate <= 0 ? null : sampleRate;

                    audioInfo = new AudioInfo
                    {
                        SampleFormat = sampleFormat,
                        SampleRate = sampleRate,
                        BitPerSample = bitPerSample
                    };
                }
                // 处理视频流
                else if (codecType == AVMediaType.AVMEDIA_TYPE_VIDEO)
                {
                    var width = codecParams->width;
                    var height = codecParams->height;
                    var pixelFormat = (AVPixelFormat)codecParams->format;

                    pictureInfo = new PictureInfo
                    {
                        Width = width,
                        Height = height,
                        PixelFormat = pixelFormat,
                    };
                }
                //其他流就不管 xxxInfo了

                // 初始化 MediaStream 并加入列表
                var mediaStream = new FfMpegReadResult.MediaStream
                {
                    Type = type,
                    Codec = codec,
                    AudioInfo = audioInfo,
                    PictureInfo = pictureInfo
                };
                streams.Add(mediaStream);
            }

            // 读取元数据
            Dictionary<string, string> metaData = new();
            AVDictionaryEntry* tag = null;
            while ((tag = ffmpeg.av_dict_get(formatContext->metadata, "", tag, ffmpeg.AV_DICT_IGNORE_SUFFIX)) != null)
            {
                var key = Marshal.PtrToStringUTF8((IntPtr)tag->key)!.ToLowerInvariant();
                var value = Marshal.PtrToStringUTF8((IntPtr)tag->value)!;
                metaData[key] = value;
            }

            // 构造最终的 FileMetaEntry
            var fileMetaEntry = new FfMpegReadResult
            {

                MetaData = metaData,
                BitRate = bitRate,
                DurationMs = durMs,
                Streams = streams.ToArray(),
            };

            err = null;
            return fileMetaEntry;
        }
        finally
        {
            // 释放资源
            ffmpeg.avformat_close_input(&formatContext);
        }
    }

}