Decoding a Speex stream

gistfile1.txt

        private Stream DecodeSpeexStream(Stream stream)
        {
            // Log function entrance
            TraceLog.TraceFunction();

            try
            {
                int totalEncoded = 0;
                int totalDecoded = 0;

                // decode all the speex-encoded chunks
                // each chunk is laid out as follows:
                // | 4-byte total chunk size | 4-byte encoded buffer size | <encoded-bytes> |
                MemoryStream ms = new MemoryStream();
                byte[] lenBytes = new byte[sizeof(int)];

                // get the length prefix
                int len = stream.Read(lenBytes, 0, lenBytes.Length);

                // loop through all the chunks
                while (len == lenBytes.Length)
                {
                    // convert the length to an int
                    int count = BitConverter.ToInt32(lenBytes, 0);
                    byte[] speexBuffer = new byte[count];
                    totalEncoded += count + len;

                    // read the chunk
                    len = stream.Read(speexBuffer, 0, count);
                    if (len < count)
                    {
                        TraceLog.TraceError(String.Format("Corrupted speex stream: len {0}, count {1}", len, count));
                        return ms;
                    }

                    // get the size of the buffer that the encoder used
                    // we need that exact size in order to properly decode
                    // the size is the first four bytes of the speexBuffer
                    int inDataSize = BitConverter.ToInt32(speexBuffer, 0);

                    // decode the chunk (starting at an offset of sizeof(int))
                    short[] decodedFrame = new short[inDataSize];
                    var speexDecoder = new SpeexDecoder(BandMode.Wide);
                    count = speexDecoder.Decode(speexBuffer, sizeof(int), len - sizeof(int), decodedFrame, 0, false);

                    // copy to a byte array
                    byte[] decodedBuffer = new byte[2 * count];
                    for (int i = 0, bufIndex = 0; i < count; i++, bufIndex += 2)
                    {
                        byte[] frame = BitConverter.GetBytes(decodedFrame[i]);
                        frame.CopyTo(decodedBuffer, bufIndex);
                    }

                    // write decoded buffer to the memory stream
                    ms.Write(decodedBuffer, 0, 2 * count);
                    totalDecoded += 2 * count;

                    // get the next length prefix
                    len = stream.Read(lenBytes, 0, lenBytes.Length);
                }

                // Log decoding stats
                TraceLog.TraceDetail(String.Format("Decoded {0} bytes into {1} bytes", totalEncoded, totalDecoded));

                // reset and return the new memory stream
                ms.Position = 0;
                return ms;
            }
            catch (Exception ex)
            {
                TraceLog.TraceException("Corrupted speex stream", ex);
                return null;
            }
        }