Add an encoder method for encoding the SPS/PPS without encoding a frame

This is useful if using a muxer that requires the SPS/PPS to be
available before the first frame is encoded.

codec/encoder/plus/inc/welsEncoderExt.h

@@ -76,6 +76,11 @@ class CWelsH264SVCEncoder : public ISVCEncoder {
   virtual int EncodeFrame (const unsigned char* kpSrc, SFrameBSInfo* pBsInfo);
   virtual int EncodeFrame (const SSourcePicture** kppSrcPicList, int nSrcPicNum, SFrameBSInfo* pBsInfo);
 
+  /*
+   * return: 0 - success; otherwise - failed;
+   */
+  virtual int EncodeParameterSets (SFrameBSInfo* pBsInfo);
+
   /*
    * return: 0 - success; otherwise - failed;
    */