DotNet 使用阿里云媒体转码服务

公司项目中一部分文件放到了阿里云 OSS 上，其中有些音频文件是 amr 类型的，在后期使用的时候比较麻烦，所以需要转换成 mp3 的文件，方便以后使用。本来想使用 ffmpeg 处理，但由于文件都存放在阿里云 OSS 上，使用 ffmpeg 就需要把文件从远程下载下来，转码之后再重新传回阿里云上，还需要使用消息组件进行通知，而且转码对服务器的压力也会很大。不如直接使用阿里云的媒体转码服务来的快，阿里云只提供了 OSS 的 DotNet 类库，并没有提供 MTS 的，所以只能自己参考 API 和其他语言的类库来开发，还好 MTS 的 API 并不是很复杂，几次尝试之后就搞定了。

相关参数需要从阿里云的控制台获取。

阿里云媒体转码服务类：

　　 /// <summary>
    /// 阿里云媒体转码服务助手类。
    /// </summary>
    public class MediaTranscodeHelper
    {

        private static readonly Encoding ENCODE_TYPE = Encoding.UTF8;
        private static readonly string ALGORITHM = "HmacSHA1";
        private static readonly string HTTP_METHOD = "GET";
        private static readonly string SEPARATOR = "&";
        private static readonly string EQUAL = "=";
        private static readonly string ISO8601_DATE_FORMAT = "yyyy-MM-dd'T'HH:mm:ss'Z'";
        private static readonly string RegionId = "cn-beijing";
        private static readonly string Version = "2014-06-18";
        private static readonly string Action = "SubmitJobs";
        private static readonly string Format = "JSON";
        private static readonly string MtsDomain = "mts.cn-beijing.aliyuncs.com";

        private static readonly int MaxRetryNumber = 3;
        private static readonly bool AutoRetry = true;
        private static readonly int TimeoutInMilliSeconds = 100000;

        private static readonly string AccessKeyId = "you AccessKeyId";
        private static readonly string AccessKeySecret = "you AccessKeySecret";
        private static readonly string PipelineId = "you PipelineId";

        /// <summary>
        /// 提交转码任务。
        /// </summary>
        /// <param name="inputFile">输入文件。</param>
        /// <returns>输出文件。</returns>
        public static string SubmitTranscodeJob(string inputFile, string ossLocation)
        {
            string outputJob = string.Empty;

            return outputJob;
        }

        /// <summary>
        /// 提交转码任务。
        /// </summary>
        public async Task<(bool success, string response)> SubmitTranscodeJob()
        {
            string SignatureNonce = Guid.NewGuid().ToString();
            var paramers = new Dictionary<string, string>
            {
                { "Action", Action },
                { "Version", "2014-06-18" },
                { "AccessKeyId", AccessKeyId },
                { "Timestamp", FormatIso8601Date(DateTime.Now) },
                { "SignatureMethod", "HMAC-SHA1" },
                { "SignatureVersion", "1.0" },
                { "SignatureNonce", SignatureNonce },
                { "Format", Format },
                { "PipelineId", PipelineId },
                { "Input", "{\"Bucket\":\"charlesbeijng\",\"Location\":\"oss-cn-beijing\",\"Object\":\"3.amr\"}" },
                { "OutputBucket", "charlesbeijng" },
                { "OutputLocation", "oss-cn-beijing" },
                { "Outputs", " [{\"OutputObject\":\"" + Guid.NewGuid().ToString() + ".mp3\",\"TemplateId\":\"1a94dc364cec44708f00367938a0122f\",\"Location\":\"oss-cn-beijing\",\"WaterMarks\":[{\"InputFile\":{\"Bucket\":\"charlesbeijng\",\"Location\":\"oss-cn-beijing\",\"Object\":\"1.png\"},\"WaterMarkTemplateId\":\"c473de87d0504f44be7ebdac1667ab13\"}]}]" }
            };

            try
            {
                string url = GetSignUrl(paramers, AccessKeySecret);

                int retryTimes = 1;
                var reply = await HttpGetAsync(url);
                while (500 <= reply.StatusCode && AutoRetry && retryTimes < MaxRetryNumber)
                {
                    url = GetSignUrl(paramers, AccessKeySecret);
                    reply = await HttpGetAsync(url);
                    retryTimes++;
                }

                if (!string.IsNullOrEmpty(reply.response))
                {
                    var res = JsonConvert.DeserializeObject<Dictionary<string, string>>(reply.response);
                    if (res != null && res.ContainsKey("Code") && "OK".Equals(res["Code"]))
                    {
                        return (true, reply.response);
                    }
                }

                return (false, reply.response);
            }
            catch (Exception ex)
            {
                return (false, response: ex.Message);
            }
        }

        /// <summary>
        /// 同步请求。
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        private static string HttpGet(string url)
        {
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
            req.Method = HTTP_METHOD;
            req.KeepAlive = true;
            req.UserAgent = "idui1";
            req.Timeout = TimeoutInMilliSeconds;
            req.ContentType = "application/x-www-form-urlencoded;charset=utf-8";
            HttpWebResponse rsp = null;
            try
            {
                rsp = (HttpWebResponse)req.GetResponse();
            }
            catch (WebException webEx)
            {
                if (webEx.Status == WebExceptionStatus.Timeout)
                {
                    rsp.Close();
                }
            }

            if (rsp != null)
            {
                if (rsp.CharacterSet != null)
                {
                    Encoding encoding = Encoding.GetEncoding(rsp.CharacterSet);
                    return GetResponseAsString(rsp, encoding);
                }
                else
                {
                    return string.Empty;
                }
            }
            else
            {
                return string.Empty;
            }
        }

        /// <summary>
        /// 异步请求。
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        private async Task<(int StatusCode, string response)> HttpGetAsync(string url)
        {
            HttpClientHandler handler = new HttpClientHandler();
            handler.Proxy = null;
            handler.AutomaticDecompression = DecompressionMethods.GZip;

            using (var http = new HttpClient(handler))
            {
                http.Timeout = new TimeSpan(TimeSpan.TicksPerMillisecond * TimeoutInMilliSeconds);
                HttpResponseMessage response = await http.GetAsync(url);
                return ((int)response.StatusCode, await response.Content.ReadAsStringAsync());
            }
        }

        /// <summary>
        /// 把响应流转换为文本。
        /// </summary>
        /// <param name="rsp">响应流对象</param>
        /// <param name="encoding">编码方式</param>
        /// <returns>响应文本</returns>
        private static string GetResponseAsString(HttpWebResponse rsp, Encoding encoding)
        {
            StringBuilder result = new StringBuilder();
            Stream stream = null;
            StreamReader reader = null;

            try
            {

                // 以字符流的方式读取HTTP响应
                stream = rsp.GetResponseStream();
                //rsp.Close();
                reader = new StreamReader(stream, encoding);

                // 每次读取不大于256个字符，并写入字符串
                char[] buffer = new char[256];
                int readBytes = 0;
                while ((readBytes = reader.Read(buffer, 0, buffer.Length)) > 0)
                {
                    result.Append(buffer, 0, readBytes);
                }
            }
            catch (WebException webEx)
            {
                if (webEx.Status == WebExceptionStatus.Timeout)
                {
                    result = new StringBuilder();
                }
            }
            finally
            {
                // 释放资源
                if (reader != null) reader.Close();
                if (stream != null) stream.Close();
                if (rsp != null) rsp.Close();
            }

            return result.ToString();
        }

        /// <summary>
        /// 处理消息。
        /// </summary>
        /// <param name="message">消息内容。</param>
        public static void HandlingMessage(string message)
        {

        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="dateTime"></param>
        /// <returns></returns>
        private static string FormatIso8601Date(DateTime dateTime)
        {
            return dateTime.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss'Z'", CultureInfo.CreateSpecificCulture("en-US"));
        }

        /// <summary>
        /// 签名
        /// </summary>
        public static string SignString(string source, string accessSecret)
        {
            using (var algorithm = new HMACSHA1(Encoding.UTF8.GetBytes(accessSecret.ToCharArray())))
            {
                return Convert.ToBase64String(algorithm.ComputeHash(Encoding.UTF8.GetBytes(source.ToCharArray())));
            }
        }

        private string GetSignUrl(Dictionary<string, string> parameters, string accessSecret)
        {
            var imutableMap = new Dictionary<string, string>(parameters)
            {
                //{ "Timestamp", FormatIso8601Date(DateTime.Now) },
                //{ "SignatureMethod", "HMAC-SHA1" },
                //{ "SignatureVersion", "1.0" },
                //{ "SignatureNonce", Guid.NewGuid().ToString() },
                //{ "Action", Action },
                //{ "Version", Version },
                //{ "Format", Format },
                //{ "RegionId", RegionId }
            };

            IDictionary<string, string> sortedDictionary = new SortedDictionary<string, string>(imutableMap, StringComparer.Ordinal);
            StringBuilder canonicalizedQueryString = new StringBuilder();
            foreach (var p in sortedDictionary)
            {
                canonicalizedQueryString.Append("&")
                .Append(PercentEncode(p.Key)).Append("=")
                .Append(PercentEncode(p.Value));
            }

            StringBuilder stringToSign = new StringBuilder();
            stringToSign.Append(HTTP_METHOD);
            stringToSign.Append(SEPARATOR);
            stringToSign.Append(PercentEncode("/"));
            stringToSign.Append(SEPARATOR);
            stringToSign.Append(PercentEncode(canonicalizedQueryString.ToString().Substring(1)));

            string signature = SignString(stringToSign.ToString(), accessSecret + "&");

            imutableMap.Add("Signature", signature);

            return ComposeUrl(MtsDomain, imutableMap);
        }
        private static string ComposeUrl(string endpoint, Dictionary<String, String> parameters)
        {
            StringBuilder urlBuilder = new StringBuilder("");
            urlBuilder.Append("http://").Append(endpoint);
            if (-1 == urlBuilder.ToString().IndexOf("?"))
            {
                urlBuilder.Append("/?");
            }
            string query = ConcatQueryString(parameters);
            return urlBuilder.Append(query).ToString();
        }
        private static string ConcatQueryString(Dictionary<string, string> parameters)
        {
            if (null == parameters)
            {
                return null;
            }
            StringBuilder sb = new StringBuilder();

            foreach (var entry in parameters)
            {
                String key = entry.Key;
                String val = entry.Value;

                sb.Append(HttpUtility.UrlEncode(key, Encoding.UTF8));
                if (val != null)
                {
                    sb.Append("=").Append(HttpUtility.UrlEncode(val, Encoding.UTF8));
                }
                sb.Append("&");
            }

            int strIndex = sb.Length;
            if (parameters.Count > 0)
                sb.Remove(strIndex - 1, 1);

            return sb.ToString();
        }

        public static string PercentEncode(string value)
        {
            StringBuilder stringBuilder = new StringBuilder();
            string text = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.~";
            byte[] bytes = Encoding.GetEncoding("UTF-8").GetBytes(value);
            foreach (char c in bytes)
            {
                if (text.IndexOf(c) >= 0)
                {
                    stringBuilder.Append(c);
                }
                else
                {
                    stringBuilder.Append("%").Append(
                        string.Format(CultureInfo.InvariantCulture, "{0:X2}", (int)c));
                }
            }
            return stringBuilder.ToString();
        }
        /// <summary>
        /// HMAC-SHA1加密算法
        /// </summary>
        /// <param name="key">密钥</param>
        /// <param name="input">要加密的串</param>
        /// <returns></returns>
        public static string HmacSha1(string key, string input)
        {
            byte[] keyBytes = Encoding.UTF8.GetBytes(key);
            byte[] inputBytes = Encoding.UTF8.GetBytes(input);
            HMACSHA1 hmac = new HMACSHA1(keyBytes);
            byte[] hashBytes = hmac.ComputeHash(inputBytes);
            return Convert.ToBase64String(hashBytes);
        }
        /// <summary>
        /// AES 算法加密(ECB模式) 将明文加密，加密后进行base64编码，返回密文
        /// </summary>
        /// <param name="EncryptStr">明文</param>
        /// <param name="Key">密钥</param>
        /// <returns>加密后base64编码的密文</returns>
        public static string Encrypt(string EncryptStr, string Key)
        {
            try
            {
                //byte[] keyArray = Encoding.UTF8.GetBytes(Key);
                byte[] keyArray = Convert.FromBase64String(Key);
                byte[] toEncryptArray = Encoding.UTF8.GetBytes(EncryptStr);

                RijndaelManaged rDel = new RijndaelManaged
                {
                    Key = keyArray,
                    Mode = CipherMode.ECB,
                    Padding = PaddingMode.PKCS7
                };

                ICryptoTransform cTransform = rDel.CreateEncryptor();
                byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);

                return Convert.ToBase64String(resultArray, 0, resultArray.Length);
            }
            catch (Exception)
            {
                return null;
            }
        }

        public static string Decrypt(string toDecrypt, string key)
        {
            byte[] keyArray = Convert.FromBase64String(key); // 将 TestGenAESByteKey 类输出的字符串转为 byte 数组
            byte[] toEncryptArray = Convert.FromBase64String(toDecrypt);
            RijndaelManaged rDel = new RijndaelManaged
            {
                Key = keyArray,
                Mode = CipherMode.ECB,        // 必须设置为 ECB
                Padding = PaddingMode.PKCS7  // 必须设置为 PKCS7
            };
            ICryptoTransform cTransform = rDel.CreateDecryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
            return Encoding.UTF8.GetString(resultArray);
        }
        private static string BuildCanonicalizedQueryString(Dictionary<string, string> parameters)
        {
            // 对参数进行排序
            List<string> sortedKeys = new List<string>(parameters.Keys);
            sortedKeys.Sort();

            StringBuilder temp = new StringBuilder();

            foreach (var key in sortedKeys)
            {
                // 此处需要对 key 和 value 进行编码
                string value = parameters[key];
                temp.Append(SEPARATOR).Append(PercentEncode(key)).Append(EQUAL).Append(PercentEncode(value));
            }
            return temp.ToString().Substring(1);
        }

        private static string BuildRequestURL(string signature, Dictionary<string, string> parameters)
        {
            // 生成请求 URL
            StringBuilder temp = new StringBuilder("mts.cn-beijing.aliyuncs.com");
            temp.Append(HttpUtility.UrlEncode("Signature", ENCODE_TYPE)).Append("=").Append(signature);
            foreach (var item in parameters)
            {
                temp.Append("&").Append(PercentEncode(item.Key)).Append("=").Append(PercentEncode(item.Value));
            }
            return temp.ToString();
        }
    }

使用的时候直接调用 SubmitTranscodeJob 方法就可以了。