diff --git a/libs/ardour/export_graph_builder.cc b/libs/ardour/export_graph_builder.cc
index 5afb5c1e7d..d9e2a60cfb 100644
--- a/libs/ardour/export_graph_builder.cc
+++ b/libs/ardour/export_graph_builder.cc
@@ -383,7 +383,7 @@ ExportGraphBuilder::Encoder::init_writer (boost::shared_ptr<AudioGrapher::CmdPip
 	 * SystemExec is deleted when writer is destroyed */
 	ARDOUR::SystemExec* exec = new ARDOUR::SystemExec (ffmpeg_exe, argp);
 	PBD::info << "Encode command: { " << exec->to_s () << "}" << endmsg;
-	if (exec->start ()) {
+	if (exec->start (SystemExec::MergeWithStdin)) {
 		throw ExportFailed ("External encoder (ffmpeg) cannot be started.");
 	}
 	writer.reset (new AudioGrapher::CmdPipeWriter<T> (exec, writer_filename));