copy ffmpeg when install-demo

@@ -216,12 +216,14 @@ uninstall:
 	@echo "rmdir \$(SRS_PREFIX)"
 	@rm -rf \$(SRS_PREFIX)
 
-install-demo:
+install-demo: install
 	@echo "mkdir \$(SRS_PREFIX)"
 	@mkdir -p \$(SRS_PREFIX)
 	@echo "copy binary files"
 	@mkdir -p \$(SRS_PREFIX)/research/api-server
 	@cp research/api-server/server.py \$(SRS_PREFIX)/research/api-server
+	@mkdir -p \$(SRS_PREFIX)/objs/ffmpeg/bin
+	@cp research/objs/ffmpeg/bin/ffmpeg \$(SRS_PREFIX)/objs/ffmpeg/bin
 	@echo "copy html files"
 	@mkdir -p \$(SRS_PREFIX)/research/api-server/static-dir/players
 	@cp research/api-server/static-dir/crossdomain.xml \$(SRS_PREFIX)/research/api-server/static-dir