Merge pull request #565 from OpenShot/fix-pts-offset-logic

Fix the PTS offset logic error when first reading a file with FFmpegReader

src/FFmpegReader.cpp

@@ -1868,8 +1868,20 @@ void FFmpegReader::UpdatePTSOffset(bool is_video) {
 		// VIDEO PACKET
 		if (video_pts_offset == 99999) // Has the offset been set yet?
 		{
-			// Find the difference between PTS and frame number (no more than 10 timebase units allowed)
-			video_pts_offset = 0 - std::max(GetVideoPTS(), (int64_t) info.video_timebase.ToInt() * 10);
+			// Find the difference between PTS and frame number
+			video_pts_offset = 0 - GetVideoPTS();
+
+			// Find the difference between PTS and frame number
+			// Also, determine if PTS is invalid (too far away from zero)
+			// We compare the PTS to the timebase value equal to 1 second (which means the PTS
+			// must be within the -1 second to +1 second of zero, otherwise we ignore it)
+			// TODO: Please see https://github.com/OpenShot/libopenshot/pull/565#issuecomment-690985272
+			// for ideas to improve this logic.
+			int64_t max_offset = info.video_timebase.Reciprocal().ToFloat();
+			if (video_pts_offset < -max_offset || video_pts_offset > max_offset) {
+				// Ignore PTS, it seems invalid
+				video_pts_offset = 0;
+			}
 
 			// debug output
 			ZmqLogger::Instance()->AppendDebugMethod("FFmpegReader::UpdatePTSOffset (Video)", "video_pts_offset", video_pts_offset, "is_video", is_video);
@@ -1878,8 +1890,18 @@ void FFmpegReader::UpdatePTSOffset(bool is_video) {
 		// AUDIO PACKET
 		if (audio_pts_offset == 99999) // Has the offset been set yet?
 		{
-			// Find the difference between PTS and frame number (no more than 10 timebase units allowed)
-			audio_pts_offset = 0 - std::max(packet->pts, (int64_t) info.audio_timebase.ToInt() * 10);
+			// Find the difference between PTS and frame number
+			// Also, determine if PTS is invalid (too far away from zero)
+			// We compare the PTS to the timebase value equal to 1 second (which means the PTS
+			// must be within the -1 second to +1 second of zero, otherwise we ignore it)
+			// TODO: Please see https://github.com/OpenShot/libopenshot/pull/565#issuecomment-690985272
+			// for ideas to improve this logic.
+			audio_pts_offset = 0 - packet->pts;
+			int64_t max_offset = info.audio_timebase.Reciprocal().ToFloat();
+			if (audio_pts_offset < -max_offset || audio_pts_offset > max_offset) {
+				// Ignore PTS, it seems invalid
+				audio_pts_offset = 0;
+			}
 
 			// debug output
 			ZmqLogger::Instance()->AppendDebugMethod("FFmpegReader::UpdatePTSOffset (Audio)", "audio_pts_offset", audio_pts_offset, "is_video", is_video);