+ double const afr = _content->active_video_frame_rate(film);
+ VideoFrameType const vft = _content->video->frame_type();
+
+ ContentTime frame_time = ContentTime::from_frames (decoder_frame, afr);
+
+ /* Do some heuristics to try and spot the case where the user sets content to 3D
+ * when it is not. We try to tell this by looking at the differences in time between
+ * the first few frames. Real 3D content should have two frames for each timestamp.
+ */
+ if (_frame_interval_checker) {
+ _frame_interval_checker->feed (frame_time, afr);
+ if (_frame_interval_checker->guess() == FrameIntervalChecker::PROBABLY_NOT_3D && vft == VIDEO_FRAME_TYPE_3D) {
+ boost::throw_exception (
+ DecodeError(
+ String::compose(
+ _("The content file %1 is set as 3D but does not appear to contain 3D images. Please set it to 2D. "
+ "You can still make a 3D DCP from this content by ticking the 3D option in the DCP video tab."),
+ _content->path(0)
+ )
+ )
+ );
+ }
+
+ if (_frame_interval_checker->guess() != FrameIntervalChecker::AGAIN) {
+ _frame_interval_checker.reset ();
+ }
+ }
+
+ Frame frame;
+ Eyes eyes = EYES_BOTH;
+ if (!_position) {
+ /* This is the first data we have received since initialisation or seek. Set
+ the position based on the frame that was given. After this first time
+ we just cound frames, since (as with audio) it seems that ContentTimes
+ are unreliable from FFmpegDecoder. They are much better than audio times
+ but still we get the occasional one which is duplicated. In this case
+ ffmpeg seems to carry on regardless, processing the video frame as normal.
+ If we drop the frame with the duplicated timestamp we obviously lose sync.
+ */
+ _position = ContentTime::from_frames (decoder_frame, afr);
+ if (vft == VIDEO_FRAME_TYPE_3D_ALTERNATE) {
+ frame = decoder_frame / 2;
+ _last_emitted_eyes = EYES_RIGHT;
+ } else {
+ frame = decoder_frame;
+ }
+ } else {
+ if (vft == VIDEO_FRAME_TYPE_3D || vft == VIDEO_FRAME_TYPE_3D_ALTERNATE) {
+ DCPOMATIC_ASSERT (_last_emitted_eyes);
+ if (_last_emitted_eyes.get() == EYES_RIGHT) {
+ frame = _position->frames_round(afr) + 1;
+ eyes = EYES_LEFT;
+ } else {
+ frame = _position->frames_round(afr);
+ eyes = EYES_RIGHT;
+ }
+ } else {
+ frame = _position->frames_round(afr) + 1;
+ }
+ }
+
+ switch (vft) {