try TH_ENCCTL_SET_DUP_COUNT but handle TH_EINVAL

src/ffmpeg2theora.c

@@ -1413,14 +1413,12 @@ void ff2theora_output(ff2theora this) {
                         if (got_picture || video_eos) {
                             prepare_ycbcr_buffer(this, ycbcr, output_buffered);
                             if(dups>0) {
-                                int _dups = dups;
-                                /*
-                                //this only works if dups is < keyint,
+                                //this only works if dups < keyint,
                                 //see http://theora.org/doc/libtheora-1.1/theoraenc_8h.html#a8bb9b05471c42a09f8684a2583b8a1df
-                                th_encode_ctl(info.td,TH_ENCCTL_SET_DUP_COUNT,&_dups,sizeof(int));
-                                */
-                                while(_dups--) {
-                                    oggmux_add_video(&info, ycbcr, video_eos);
+                                if (th_encode_ctl(info.td,TH_ENCCTL_SET_DUP_COUNT,&dups,sizeof(int)) == TH_EINVAL) {
+                                    int _dups = dups;
+                                    while(_dups--)
+                                        oggmux_add_video(&info, ycbcr, video_eos);
                                 }
                             }
                             oggmux_add_video(&info, ycbcr, video_eos);