Hi!!
in VLC you can see the video frame rate with "Ctrl-j", and check if it was produced at 30fps (in sub-folder codec)
May be your computer experiment some lack of CPU/memory when was producing
did you try to produce again?
don't worry for the english, much people have not 'english' as native tongue Daniel Saxer
Asus GT750
i74700 2.4 + GTX770M + 16Gb ram

thank you for interest : ,
I think the problem is in the file because i've noticed the problem working in a project with many files.
I opened and closed PDR various times but the problem is still there.
I've tried also to to delete shadowed files generated by PDR but the problem returns...

Then i've tried to create a new project with only the file with problem and the problem comes out in the same position (at the same minute,second of the source file) even if the position of the file is different in the two projects.

I haven't tried to encode file in another format before import in PDR, and I prefer not to encode files before editing to mantain a good quality of results and to save time

The strange thing is that in VLC and WMP the original file plays good, without visible gaps.

Tomorrow i'll try to re-encode the file to se if something changes.

thankyou and see ya in cyberspace!

You may already know this, but if not:

Click on the gear to set "Preferences". On the first tab (general) you can set the frame rate (to 30 in your case). Then you can either use "drop-frame" or not. If not, you'll have 30 fps. If so, you'll have 29.97.

Hope this helps.

P.S. My avatar photo was taken in Montepulciano...hence the big smile! Regards,
Dan
Power Director 21-Ultimate
v 21.0.3111.0
XPS-8940, Win-10 64-bit,
Intel Core i9-10900 processor
(10 core, 20M Cache),
32GB DDR4 RAM, 2TB M.2 PCIe NVME SSD, 2TB 7200 RPM SATA HDD,
NVIDIA GeForce RTX 2060 SUPER 8GB GDDR6

ahhhhhh, finally someone explained me what is the meaning of that checkbox
I made a search with google but didn't found an explanation so immediate and clear.

thankyou very much.

P.S.
VLC with ctrl+J tells me the file is 30fps so in the preferences of PD i will not check the drop frames checkbox. right?

Right. If you don't check drop frame, you'll have 30fps (or whatever you have selected as frame rate.)

P.S. I changed my avatar...the current one was not taken in Montepulciano (hence the lack of a big smile). Regards,
Dan
Power Director 21-Ultimate
v 21.0.3111.0
XPS-8940, Win-10 64-bit,
Intel Core i9-10900 processor
(10 core, 20M Cache),
32GB DDR4 RAM, 2TB M.2 PCIe NVME SSD, 2TB 7200 RPM SATA HDD,
NVIDIA GeForce RTX 2060 SUPER 8GB GDDR6

Many thanks,
i've set the "drop frame timecode" to NO, so the timeline will run at 30.00fps: the same of the video source. But PDR still alert me that timeline frame rate differs from the clip.... the message appears even if the value of setting is YES I don't know what think about this alert...

I attached 3 images of :
- program settings (30fps)
- alert message
- info about clip

The problem of frames freezed is VERY VERY strange... i've made some tests and re-encoded the clip in another .mp4 file with with the same codec (H264 AVC) with same fps, same resolution, higher video bitrate and higher audio bitrate (to loose less details as possible).
I've replaced in timeline the problematic file with the re-encoded and the problem vanished. Then i reinserted the original file and the problem returned....
So I understand the original file has some problems in his stream, but I don't get a sense of why VLC & WMP plays the file fine.

In PDR i can scroll the video by one frame at time and at the problematic frame i can see 9 frames replicated. In VLC i can also move cursor by one frame at time an I can see the real frames "hidden" in PDR.

Excuse me for the verbose response, maybe i'ts a way to train my english

In conclusion of this strange experience, i solved it re-encoding the file but is not the right way to solve and comprehend the problem. I believe in future I will encounter other times this oddity almost until I will buy another ActionCam ...

Thankyou all Dan, Daniel and MPEG_Streamclip (for free reencoding) :

P.S.
the avatar taken in Montepulciano was better than your last