Having trouble merging video files together

[gutterboy333]

I'm trying to merge multiple video files together (4), they are about 30mins long and around 550mb each on average, and are MP4 files.

Thing is, I am having trouble doing so.

I tried Avidemux, but whenever I load one of the files, I get a message saying..

This video contains B-frames, but presentation time stamps (PTS) are either missing or monotonically increasing. Avidemex can try to reconstruct correct PTS by decoding the entire video. This may take a lot of time. Proceed?

Now, I have no idea what this actually means, and Googling it found other people with the issue, but not much of an explanation of what it actually means.

If I select "No" and merge the videos anyway, will the video be messed up in some way - or what will the issue be?

Next up I tried MP4Tools - was able to load the files into it with no issues, but after a few mins of it processing the files once I started to merge them, my computer started "beeping" at me, with some long constant beep. I have never seen my PC do this before, and have no idea what it meant.

So I stopped it and tried it again, but same issue.

I have come across a few paid programs, but haven't tried any yet - and I have no issues purchasing a program if it's not too expensive, but obviously if there a free program that can do the job then all the better.

Thanks a lot.

[ProWo]

You can try clever FFmpeg-GUI.
Load your first mp4. click main, click Join, the first mp4 is already loaded, drag & drop the other 3 mp4 files (one after one to mantain the correct order) and click join.
If finished, you'll find the new joined mp4 file into the target folder.

[gutterboy333]

Thanks very much. Got it to work

[mrbass]

Losslesscut and videomass merge audio or video files quite well too.

[SamNYC]

It looks like you're somewhat of a beginner. Well, I'm two notches below that so take my answer with a huge grain of salt...
.
From what I understand, B-frames contain information about the frames before and after it. That allows Avidemux to make slightly better compressions, and at a faster speed.

To confirm this, I found a 5GB file where Avidemux gives the B-frame warning. My project is to convert and compress the file to x265. I first said Yes to recreating the B-frames. The re-creation took much longer than the procedure normally does, about 4 mins. It usually takes only a minute or so. I then proceeded to compress.

Then I loaded the file again and said No to the B-frame re-creation, and then compressed. Although I saved the 4 mins it took to re-creating B-frames, the entire compression took much longer. I didn't time the operations but the latter was definitely longer.

My conclusion is that the B-frame re-creation is optional. It simply makes the compression more efficient. As for concatenating the files, the same thing applies. You can choose Yes or No, and the program won't crash. The parts of the merged file that have B-frames will compress faster.

I welcome corrections and clarification from people who know better than me!