- // The snapping above makes us lock to the input framerate, even in the presence
- // of pts drift, for most typical cases where it's needed, like converting 60 → 2x60
- // or 60 → 2x59.94. However, there are some corner cases like 25 → 2x59.94, where we'd
- // get a snap very rarely (in the given case, once every 24 output frames), and by
- // that time, we'd have drifted out. We could have solved this by changing the overall
- // speed ever so slightly, but it requires that we know the actual frame rate (which
- // is difficult in the presence of jitter and missed frames), or at least do some kind
- // of matching/clustering. Instead, we take the opportunity to lock to in-between rational
- // points if we can. E.g., if we are converting 60 → 2x60, we would not only snap to
- // an original frame every other frame; we would also snap to exactly alpha=0.5 every
- // in-between frame. Of course, we will still need to interpolate, but we get a lot
- // closer when we actually get close to an original frame. In other words: Snap more
- // often, but snap less each time. Unless the input and output frame rates are completely
- // decorrelated with no common factor, of course (e.g. 12.345 → 34.567, which we should
- // really never see in practice).
- for (double fraction : { 1.0 / 2.0, 1.0 / 3.0, 2.0 / 3.0, 1.0 / 4.0, 3.0 / 4.0,
- 1.0 / 5.0, 2.0 / 5.0, 3.0 / 5.0, 4.0 / 5.0 }) {
- double subsnap_pts = frame_lower.pts + fraction * (frame_upper.pts - frame_lower.pts);
- if (fabs(subsnap_pts - in_pts) < pts_snap_tolerance) {
- in_pts_origin += lrint(subsnap_pts) - in_pts;
- in_pts = lrint(subsnap_pts);
- break;
+ // Snap to input frame: If we can do so with less than 1% jitter
+ // (ie., move less than 1% of an _output_ frame), do so.
+ // TODO: Snap secondary (fade-to) clips in the same fashion.
+ double pts_snap_tolerance = 0.01 * double(TIMEBASE) / global_flags.output_framerate;
+ bool snapped = false;
+ for (FrameOnDisk snap_frame : { frame_lower, frame_upper }) {
+ if (fabs(snap_frame.pts - in_pts) < pts_snap_tolerance) {
+ auto display_func = [this, primary_stream_idx, snap_frame, secondary_frame, fade_alpha]{
+ if (destination != nullptr) {
+ destination->setFrame(primary_stream_idx, snap_frame, secondary_frame, fade_alpha);
+ }
+ };
+ if (video_stream == nullptr) {
+ display_func();
+ } else {
+ if (secondary_stream_idx == -1) {
+ ++metric_original_snapped_frame;
+ video_stream->schedule_original_frame(
+ next_frame_start, pts, display_func,
+ QueueSpotHolder(this), snap_frame);
+ } else {
+ assert(secondary_frame.pts != -1);
+ ++metric_faded_snapped_frame;
+ video_stream->schedule_faded_frame(
+ next_frame_start, pts, display_func, QueueSpotHolder(this),
+ snap_frame, secondary_frame, fade_alpha);
+ }
+ }
+ in_pts_origin += snap_frame.pts - in_pts;
+ snapped = true;
+ last_pts_played = snap_frame.pts;
+ break;
+ }
+ }
+ if (snapped) {
+ continue;