From c2adc362e4ce0a64d7e7a1c6b634b024d862c8c1 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Sat, 21 Feb 2026 02:37:42 +0100
Subject: Handle FFmpeg content with only subtitles enabled better.

Previously if some FFmpeg content was set to use only its subtitles, and
the first subtitle was 1 minute in to the content, the content would be
selected for pass() until its first minute had been scanned.

This could be slow, and incorrect as on the way to this 1 minute we want
to look at other content.

Here we store the PTS of dropped packets to use as a fallback position
when there is no video or audio enabled.
---
 src/lib/ffmpeg_decoder.cc | 40 ++++++++++++++++++++++++++++++++++++++++
 src/lib/ffmpeg_decoder.h  |  3 +++
 2 files changed, 43 insertions(+)

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index ec85bb56c..294db777d 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -102,6 +102,8 @@ FFmpegDecoder::FFmpegDecoder (shared_ptr<const Film> film, shared_ptr<const FFmp
 	for (auto i: c->ffmpeg_audio_streams()) {
 		_next_time[i] = boost::optional<dcpomatic::ContentTime>();
 	}
+
+	_dropped_time.resize(_format_context->nb_streams);
 }
 
 
@@ -240,6 +242,9 @@ FFmpegDecoder::pass ()
 		decode_and_process_subtitle_packet (packet);
 	} else if (audio) {
 		decode_and_process_audio_packet (packet);
+	} else {
+		DCPOMATIC_ASSERT(static_cast<int>(_dropped_time.size()) > si);
+		_dropped_time[si] = dcpomatic::ContentTime::from_seconds(packet->pts * av_q2d(_format_context->streams[si]->time_base) + _pts_offset.seconds());
 	}
 
 	if (_have_current_subtitle && _current_subtitle_to && position() > *_current_subtitle_to) {
@@ -466,6 +471,10 @@ FFmpegDecoder::seek (ContentTime time, bool accurate)
 	for (auto& i: _next_time) {
 		i.second = boost::optional<dcpomatic::ContentTime>();
 	}
+
+	for (auto& dropped: _dropped_time) {
+		dropped = boost::none;
+	}
 }
 
 
@@ -846,3 +855,34 @@ FFmpegDecoder::process_ass_subtitle (string ass, ContentTime from)
 		only_text()->emit_plain_start (from, i);
 	}
 }
+
+
+ContentTime
+FFmpegDecoder::position() const
+{
+	optional<ContentTime> pos;
+	auto f = film();
+
+	if (video && !video->ignore() && (!pos || video->position(f).get_value_or(ContentTime()) < *pos)) {
+		pos = video->position(f);
+	}
+
+	if (audio && !audio->ignore() && (!pos || audio->position(f).get_value_or(ContentTime()) < *pos)) {
+		pos = audio->position(f);
+	}
+
+	if (!pos) {
+		for (auto dropped: _dropped_time) {
+			if (dropped) {
+				if (pos) {
+					pos = std::min(*pos, *dropped);
+				} else {
+					pos = *dropped;
+				}
+			}
+		}
+	}
+
+	return pos.get_value_or(ContentTime());
+}
+
diff --git a/src/lib/ffmpeg_decoder.h b/src/lib/ffmpeg_decoder.h
index bd4b74f88..022c5625b 100644
--- a/src/lib/ffmpeg_decoder.h
+++ b/src/lib/ffmpeg_decoder.h
@@ -53,6 +53,7 @@ public:
 
 	bool pass () override;
 	void seek (dcpomatic::ContentTime time, bool) override;
+	dcpomatic::ContentTime position() const override;
 
 private:
 	friend struct ::ffmpeg_pts_offset_test;
@@ -102,4 +103,6 @@ private:
 	};
 
 	FlushState _flush_state = FlushState::CODECS;
+
+	std::vector<boost::optional<dcpomatic::ContentTime>> _dropped_time;
 };
-- 
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