Fix errors when seeking FFmpeg for some formats.

The comments discuss this in a bit more depth, but basically we see
errors from avcodec_send_packet after seek.  ffplay etc. seem basically
to ignore all errors from avcodec_send_packet, and I can't find a
"proper" fix, so here's a half-way house hack: ignore some errors
after seek.  Nasty.

3 files changed, 16 insertions, 0 deletions

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index c5c41fdac..31fbde773 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -427,6 +427,12 @@ FFmpegDecoder::seek (ContentTime time, bool accurate)
 	for (auto& i: _next_time) {
 		i.second = boost::optional<dcpomatic::ContentTime>();
 	}
+
+	/* We find that we get some errors from av_send_packet after a seek.  Perhaps we should ignore
+	 * all of them (which seems risky), or perhaps we should have some proper fix.  But instead
+	 * let's ignore the next 2 errors.
+	 */
+	_errors_to_ignore = 2;
 }
 
 
@@ -513,6 +519,12 @@ FFmpegDecoder::decode_and_process_audio_packet (AVPacket* packet)
 		/* We could cope with AVERROR(EAGAIN) and re-send the packet but I think it should never happen.
 		 * Likewise I think AVERROR_EOF should not happen.
 		 */
+		if (_errors_to_ignore > 0) {
+			/* We see errors here after a seek, which is hopefully to be nothing to worry about */
+			--_errors_to_ignore;
+			LOG_GENERAL("Ignoring error %1 avcodec_send_packet after seek; will ignore %2 more", r, _errors_to_ignore);
+			return;
+		}
 		throw DecodeError (N_("avcodec_send_packet"), N_("FFmpegDecoder::decode_and_process_audio_packet"), r);
 	}
 
diff --git a/src/lib/ffmpeg_decoder.h b/src/lib/ffmpeg_decoder.h
index fce3fcae9..def824feb 100644
--- a/src/lib/ffmpeg_decoder.h
+++ b/src/lib/ffmpeg_decoder.h
@@ -79,6 +79,9 @@ private:
 	/** true if we have a subtitle which has not had emit_stop called for it yet */
 	bool _have_current_subtitle = false;
 
+	/** number of errors from avcodec_send_packet to ignore */
+	int _errors_to_ignore = 0;
+
 	std::shared_ptr<Image> _black_image;
 
 	std::map<std::shared_ptr<FFmpegAudioStream>, boost::optional<dcpomatic::ContentTime>> _next_time;
diff --git a/test/ffmpeg_decoder_seek_test.cc b/test/ffmpeg_decoder_seek_test.cc
index f8ce256cf..4dceae86b 100644
--- a/test/ffmpeg_decoder_seek_test.cc
+++ b/test/ffmpeg_decoder_seek_test.cc
@@ -100,4 +100,5 @@ BOOST_AUTO_TEST_CASE (ffmpeg_decoder_seek_test)
 	test ("boon_telly.mkv", frames);
 	test ("Sintel_Trailer1.480p.DivX_Plus_HD.mkv", frames);
 	test ("prophet_long_clip.mkv", { 15, 42, 999, 15 });
+	test ("dolby_aurora.vob", { 0, 125, 250, 41 });
 }