From ca21cc2099526b68b9663d39c4e402c7faee7c5e Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Sun, 16 Feb 2020 21:15:12 +0100
Subject: [PATCH] Better errors if butler doesn't give video during export.

---
 src/lib/ffmpeg_encoder.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/lib/ffmpeg_encoder.cc b/src/lib/ffmpeg_encoder.cc
index 4614903db..0233632d7 100644
--- a/src/lib/ffmpeg_encoder.cc
+++ b/src/lib/ffmpeg_encoder.cc
@@ -141,7 +141,11 @@ FFmpegEncoder::go ()
 		}
 
 		for (int j = 0; j < gets_per_frame; ++j) {
-			pair<shared_ptr<PlayerVideo>, DCPTime> v = _butler->get_video ();
+			Butler::Error e;
+			pair<shared_ptr<PlayerVideo>, DCPTime> v = _butler->get_video (&e);
+			if (!v.first) {
+				throw ProgrammingError(__FILE__, __LINE__, String::compose("butler returned no video; error was %1", static_cast<int>(e)));
+			}
 			shared_ptr<FFmpegFileEncoder> fe = encoder->get (v.first->eyes());
 			if (fe) {
 				fe->video(v.first, v.second);
-- 
2.30.2