From: Carl Hetherington <cth@carlh.net>
Date: Sun, 12 Sep 2021 20:43:52 +0000 (+0200)
Subject: Fix missing subtitles embedded in files decoded by FFmpeg (#2060).
X-Git-Tag: v2.15.161~1
X-Git-Url: https://main.carlh.net/gitweb/?p=dcpomatic.git;a=commitdiff_plain;h=60450bd93af0b331d7b98c88aa199366305f0721

Fix missing subtitles embedded in files decoded by FFmpeg (#2060).

Since the FFmpeg 4.4 update it seems that AVSubtitle::pts is no longer
set (it's AV_NOPTS_VALUE, i think).

Instead we apparently need to get the PTS from the packet, which in
turn requires the stream's timebase.
---

diff --git a/src/lib/ffmpeg.cc b/src/lib/ffmpeg.cc
index d476b4c29..31aa18293 100644
--- a/src/lib/ffmpeg.cc
+++ b/src/lib/ffmpeg.cc
@@ -284,9 +284,9 @@ FFmpeg::avio_seek (int64_t const pos, int whence)
 
 
 FFmpegSubtitlePeriod
-FFmpeg::subtitle_period (AVSubtitle const & sub)
+FFmpeg::subtitle_period (AVPacket const* packet, AVStream const* stream, AVSubtitle const & sub)
 {
-	auto const packet_time = ContentTime::from_seconds (static_cast<double> (sub.pts) / AV_TIME_BASE);
+	auto const packet_time = ContentTime::from_seconds (packet->pts * av_q2d(stream->time_base));
 
 	if (sub.end_display_time == static_cast<uint32_t> (-1)) {
 		/* End time is not known */
diff --git a/src/lib/ffmpeg.h b/src/lib/ffmpeg.h
index 58223fa97..b0769971e 100644
--- a/src/lib/ffmpeg.h
+++ b/src/lib/ffmpeg.h
@@ -36,6 +36,7 @@ DCPOMATIC_ENABLE_WARNINGS
 
 struct AVFormatContext;
 struct AVFrame;
+struct AVStream;
 struct AVIOContext;
 
 class FFmpegContent;
@@ -63,7 +64,7 @@ protected:
 		std::vector<std::shared_ptr<FFmpegAudioStream>> audio_streams, boost::optional<dcpomatic::ContentTime> first_video, double video_frame_rate
 		) const;
 
-	static FFmpegSubtitlePeriod subtitle_period (AVSubtitle const & sub);
+	static FFmpegSubtitlePeriod subtitle_period (AVPacket const* packet, AVStream const* stream, AVSubtitle const & sub);
 
 	std::shared_ptr<const FFmpegContent> _ffmpeg_content;
 
diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index 3202dcd3e..72372fca8 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -622,12 +622,14 @@ FFmpegDecoder::decode_and_process_subtitle_packet (AVPacket* packet)
 		return;
 	}
 
+	auto sub_period = subtitle_period (packet, ffmpeg_content()->subtitle_stream()->stream(_format_context), sub);
+
 	/* Stop any current subtitle, either at the time it was supposed to stop, or now if now is sooner */
 	if (_have_current_subtitle) {
 		if (_current_subtitle_to) {
-			only_text()->emit_stop (min(*_current_subtitle_to, subtitle_period(sub).from + _pts_offset));
+			only_text()->emit_stop (min(*_current_subtitle_to, sub_period.from + _pts_offset));
 		} else {
-			only_text()->emit_stop (subtitle_period(sub).from + _pts_offset);
+			only_text()->emit_stop (sub_period.from + _pts_offset);
 		}
 		_have_current_subtitle = false;
 	}
@@ -641,7 +643,6 @@ FFmpegDecoder::decode_and_process_subtitle_packet (AVPacket* packet)
 	/* Subtitle PTS (within the source, not taking into account any of the
 	   source that we may have chopped off for the DCP).
 	*/
-	auto sub_period = subtitle_period (sub);
 	ContentTime from;
 	from = sub_period.from + _pts_offset;
 	if (sub_period.to) {