ExtendScript: `track.insertClip` placement offset depends on clip framerate

Steps to reproduce the issue:

1. Say we have two clips: one at 16 fps and the same at 60 fps. I'll also attach a second pair of files: scene1_16fps.mp4, scene1_60fps.mp4, scene2_16fps.mp4, scene2_60fps.mp4. Just in case, I'll attach MediaInfo for the files.

   Complete name               : D:\temp\scene1_16fps.mp4
   Format                      : MPEG-4
   Format profile              : Base Media
   Codec ID                    : isom (isom/iso2/avc1/mp41)
   File size                   : 8.82 MiB
   Duration                    : 5 s 63 ms
   Overall bit rate            : 14.6 Mb/s
   Frame rate                  : 16.000 FPS
   Writing application         : Lavf61.1.100
   
   Video
   ID                          : 1
   Format                      : AVC
   Format/Info                 : Advanced Video Codec
   Format profile              : High@L3.1
   Format settings             : CABAC / 4 Ref Frames
   Format settings, CABAC      : Yes
   Format settings, Reference  : 4 frames
   Codec ID                    : avc1
   Codec ID/Info               : Advanced Video Coding
   Duration                    : 5 s 63 ms
   Bit rate                    : 14.6 Mb/s
   Width                       : 720 pixels
   Height                      : 1 280 pixels
   Display aspect ratio        : 0.563
   Frame rate mode             : Constant
   Frame rate                  : 16.000 FPS
   Color space                 : YUV
   Chroma subsampling          : 4:2:0
   Bit depth                   : 8 bits
   Scan type                   : Progressive
   Bits/(Pixel*Frame)          : 0.991
   Stream size                 : 8.82 MiB (100%)
   Writing library             : x264 core 164 r3191 4613ac3
   Encoding settings           : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=32 / lookahead_threads=5 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=16 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=10.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
   Codec configuration box     : avcC

    

2. Create a sequence at 60 fps. Place all the mp4s into the Project.
3. Run the code:

   var project = app.project;
   var rootItem = project.rootItem;
   var scene1_16fps_item = rootItem.children[0];
   var scene2_16fps_item = rootItem.children[1];
   var scene1_60fps_item = rootItem.children[2];
   var scene2_60fps_item = rootItem.children[3];
   
   var seq = project.activeSequence
   var track = seq.videoTracks[0]
   var track2 = seq.videoTracks[1]
   // remove all
   for (var i = track.clips.numItems - 1; i >= 0; i--) {
       var clip = track.clips[i];
       clip.remove(false, false); 
   }
   for (var i = track2.clips.numItems - 1; i >= 0; i--) {
       var clip = track2.clips[i];
       clip.remove(false, false);
   }
   
   var time = new Time()
   var targetSeconds = 0.3749
   //var targetSeconds = 0.38;
   var targetTicks = targetSeconds * 254016000000;
   time.ticks = targetTicks.toString()
   
   scene1_16fps_item.setOutPoint(time, 1)
   var newClip11 = track.insertClip(scene1_16fps_item, 0);
   
   scene1_60fps_item.setOutPoint(time, 1)
   var newClip21 = track2.insertClip(scene1_60fps_item, 0);
   
   var newClip12 = track.insertClip(scene1_16fps_item, time);
   var newClip22 = track2.insertClip(scene1_60fps_item, time);
   

   What it does: places the first clip scene1 starting at frame 0, cut at 0.3749s. Then places the next two clips at the same time offset.

4. Expected behavior: first clip ends at 0.3749 × 60 = 22.494 ≈ 22 frames. Next clip starts immediately after.
   Actual behavior: 60 fps clips are placed correctly; 16 fps clip has a gap of 4 (!) frames.
    

   

    

5. You can change the value to 0.38 and see that both first clips end at frame 22 and both second clips start one frame later - which is also incorrect.
    

   

    

6. No matter what I try, I always get missing frames (1-4) whenever I have a clip whose out-point ends at time X (while the source is longer than X) and the next clip starts at the same X. I also tried exotic formulas like var roundedSeconds = Math.round(targetSeconds * srcFps) / srcFps, but that didn't help either.

   Any ideas what math is happening under the hood? How do I place clips without gaps, matching my script's time data, using ExtendScript?