C# FFmepg API [Unable to load DLL 'avcodec.59 under ]の対処方法が知りたい

提示コードですが以下のここですのコード部で以下のError部の例外が発生します。これはなぜでしょうか？dllは追加しています。ファイル名をavcodec.59やavcodec.59.dll等に名前を変更しましたがロードされません。またinput.flacのファイルが.exeと同じ場所にあります。
何が原因で.dllファイルが読めないのでしょうか？

dllファイル:https://www.dlldownloader.com/avcodec-dll/

参考コード: https://github.com/Ruslan-B/FFmpeg.AutoGen/blob/master/FFmpeg.AutoGen.Examples.Encode/Program.cs

Error

System.DllNotFoundException: 'Unable to load DLL 'avcodec.59 under C:\Users\yw325\Desktop\ConsoleApp1\ConsoleApp1\bin\Debug\net6.0\': The specified module could not be found.'

cs

using FFmpeg.AutoGen; internal unsafe class Program{ static int Main(string[] args) { AVFrame* frame; AVPacket* pkt; int i, j, k, ret; short* samples; float t, tincr; if (args.Length <= 0) { string executable = Environment.GetCommandLineArgs()[0]; //Console.Error.WriteLine($"Usage: {executable} <output file>"); //return 0; } var filename = "input.flac"; /* find the MP2 encoder */ AVCodec* codec = ffmpeg.avcodec_find_encoder(AVCodecID.AV_CODEC_ID_MP2);//ここです。 if (codec == null) { Console.Error.WriteLine("Codec not found"); return 1; } AVCodecContext* c = ffmpeg.avcodec_alloc_context3(codec); if (c == null) { Console.Error.WriteLine("Could not allocate audio codec context"); return 1; } /* put sample parameters */ c->bit_rate = 64000; /* check that the encoder supports s16 pcm input */ c->sample_fmt = AVSampleFormat.AV_SAMPLE_FMT_S16; if (!check_sample_fmt(codec, c->sample_fmt)) { string sampleFormat = ffmpeg.av_get_sample_fmt_name(c->sample_fmt); Console.Error.WriteLine($"Encoder does not support sample format {sampleFormat}"); return 1; } /* select other audio parameters supported by the encoder */ c->sample_rate = select_sample_rate(codec); c->channel_layout = select_channel_layout(codec); c->channels = ffmpeg.av_get_channel_layout_nb_channels(c->channel_layout); /* open it */ if (ffmpeg.avcodec_open2(c, codec, null) < 0) { Console.Error.WriteLine($"Could not open codec"); return 1; } using BinaryWriter output = new BinaryWriter(new FileStream(filename, FileMode.Create)); /* packet for holding encoded output */ pkt = ffmpeg.av_packet_alloc(); if (pkt == null) { Console.Error.WriteLine($"could not allocate the packet"); return 1; } /* frame containing input raw audio */ frame = ffmpeg.av_frame_alloc(); if (frame == null) { Console.Error.WriteLine($"Could not allocate audio frame"); return 1; } frame->nb_samples = c->frame_size; frame->format = (int)c->sample_fmt; frame->channel_layout = c->channel_layout; /* allocate the data buffers */ ret = ffmpeg.av_frame_get_buffer(frame, 0); if (ret < 0) { Console.Error.WriteLine($"Could not allocate audio data buffers"); return 1; } /* encode a single tone sound */ t = 0.0f; tincr = (float)(2 * Math.PI * 440.0 / c->sample_rate); for (i = 0; i < 200; i++) { /* make sure the frame is writable -- makes a copy if the encoder * kept a reference internally */ ret = ffmpeg.av_frame_make_writable(frame); if (ret < 0) return 1; samples = (short*)frame->data[0]; for (j = 0; j < c->frame_size; j++) { samples[2 * j] = (short)(Math.Sin(t) * 10000); for (k = 1; k < c->channels; k++) samples[2 * j + k] = samples[2 * j]; t += tincr; } encode(c, frame, pkt, output); } /* flush the encoder */ encode(c, null, pkt, output); ffmpeg.av_frame_free(&frame); ffmpeg.av_packet_free(&pkt); ffmpeg.avcodec_free_context(&c); return 0; } static void encode(AVCodecContext* ctx, AVFrame* frame, AVPacket* pkt, BinaryWriter output) { int ret; /* send the frame for encoding */ ret = ffmpeg.avcodec_send_frame(ctx, frame); if (ret < 0) { Console.Error.WriteLine($"Error sending the frame to the encoder"); Environment.Exit(1); } /* read all the available output packets (in general there may be any * number of them */ while (ret >= 0) { ret = ffmpeg.avcodec_receive_packet(ctx, pkt); if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN) || ret == ffmpeg.AVERROR_EOF) return; else if (ret < 0) { Console.Error.WriteLine($"Error encoding audio frame"); Environment.Exit(1); } output.Write(new ReadOnlySpan<byte>(pkt->data, pkt->size)); ffmpeg.av_packet_unref(pkt); } } /* check that a given sample format is supported by the encoder */ static bool check_sample_fmt(AVCodec* codec, AVSampleFormat sample_fmt) { AVSampleFormat* p = codec->sample_fmts; while (*p != AVSampleFormat.AV_SAMPLE_FMT_NONE) { if (*p == sample_fmt) return true; p++; } return false; } /* just pick the highest supported samplerate */ static int select_sample_rate(AVCodec* codec) { int best_samplerate = 0; if (codec->supported_samplerates == null) return 44100; int* p = codec->supported_samplerates; while (*p != 0) { if (best_samplerate != 0 || Math.Abs(44100 - *p) < Math.Abs(44100 - best_samplerate)) best_samplerate = *p; p++; } return best_samplerate; } /* select layout with the highest channel count */ static ulong select_channel_layout(AVCodec* codec) { ulong* p; ulong best_ch_layout = 0; int best_nb_channels = 0; if (codec->channel_layouts == null) return ffmpeg.AV_CH_LAYOUT_STEREO; p = codec->channel_layouts; while (*p != 0) { int nb_channels = ffmpeg.av_get_channel_layout_nb_channels(*p); if (nb_channels > best_nb_channels) { best_ch_layout = *p; best_nb_channels = nb_channels; } p++; } return best_ch_layout; }}