private int Read(byte[] buffer, int offset, int count)
{
System.Diagnostics.Debug.Assert(buffer != null);
System.Diagnostics.Debug.Assert(0 <= offset && offset < buffer.Length);
System.Diagnostics.Debug.Assert(0 < count && count <= buffer.Length - offset);
EnsureOutputData();
var fetched = mDecoder.ReadOutputData(buffer, offset, count);
System.Diagnostics.Debug.Assert(0 <= fetched && fetched <= count);
mPosition += fetched;
return(fetched);
}