C#實戰小技巧（十三）：獲取WAV音頻文件信息和音頻時長

通過讀取wav文件流，可獲取音頻文件時長等信息。
根據wav文件信息格式，構造下面的結構體，用於保存文件信息：

	/// <summary>
    /// WAV文件信息
    /// </summary>
    public struct WavInfo
    {
        public string groupid;
        public string rifftype;
        public long filesize;
        public string chunkid;
        public long chunksize;
        public short wformattag; //記錄着此聲音的格式代號
        public ushort wchannels; //記錄聲音的頻道數。
        public ulong dwsamplespersec;//記錄每秒取樣數。
        public ulong dwavgbytespersec;//記錄每秒的數據量。
        public ushort wblockalign;//記錄區塊的對齊單位。
        public ushort wbitspersample;//記錄每個取樣所需的位元數。
        public string datachunkid;
        public long datasize;
    }

讀取wav文件流後，根據信息格式解析出文件信息：

		/// <summary>
        /// 獲取WAV文件信息
        /// </summary>
        /// <param name="fileName">文件路徑</param>
        /// <returns></returns>
        private WavInfo GetWavInfo(string fileName)
        {
            WavInfo wavInfo = new WavInfo();
            FileInfo fi = new FileInfo(fileName);
            using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
            {
                if (fs.Length >= 44)
                {
                    byte[] bInfo = new byte[44];
                    fs.Read(bInfo, 0, 44);
                    Encoding.Default.GetString(bInfo, 0, 4);
                    if (Encoding.Default.GetString(bInfo, 0, 4) == "RIFF" && Encoding.Default.GetString(bInfo, 8, 4) == "WAVE" && Encoding.Default.GetString(bInfo, 12, 4) == "fmt ")
                    {
                        wavInfo.groupid = Encoding.Default.GetString(bInfo, 0, 4);
                        System.BitConverter.ToInt32(bInfo, 4);
                        wavInfo.filesize = System.BitConverter.ToInt32(bInfo, 4);
                        wavInfo.rifftype = Encoding.Default.GetString(bInfo, 8, 4);
                        wavInfo.chunkid = Encoding.Default.GetString(bInfo, 12, 4);
                        wavInfo.chunksize = System.BitConverter.ToInt32(bInfo, 16);
                        wavInfo.wformattag = System.BitConverter.ToInt16(bInfo, 20);
                        wavInfo.wchannels = System.BitConverter.ToUInt16(bInfo, 22);
                        wavInfo.dwsamplespersec = System.BitConverter.ToUInt32(bInfo, 24);
                        wavInfo.dwavgbytespersec = System.BitConverter.ToUInt32(bInfo, 28);
                        wavInfo.wblockalign = System.BitConverter.ToUInt16(bInfo, 32);
                        wavInfo.wbitspersample = System.BitConverter.ToUInt16(bInfo, 34);
                        wavInfo.datachunkid = Encoding.Default.GetString(bInfo, 36, 4);
                        wavInfo.datasize = System.BitConverter.ToInt32(bInfo, 40);
                    }
                }
            }

            return wavInfo;
        }

獲取wav文件信息後，可計算出音頻時長：

		/// <summary>
        /// 獲取音頻文件長度
        /// </summary>
        /// <param name="fileName">文件路徑</param>
        /// <returns>返回單位(秒)</returns>
        private int GetVoiceDuration(string fileName)
        {
            int duration = 0;
            try
            {
                WavInfo wavInfo = this.GetWavInfo(fileName);
                duration = Convert.ToInt32(wavInfo.datasize / Convert.ToInt64(wavInfo.dwavgbytespersec));
            }
            catch (Exception ex)
            {
                LOG.Error(new StringBuilder("獲取音頻文件長度出錯：").Append(fileName).Append(", ").Append(ex.Message));
            }

            return duration;
        }