Occasional issue with merging FLV fragments from Nick.com

[CyrusVBA]

Hi, this is my first time posting here.

I want to ask your advice on how to deal with the issue I'm having.

I'm using rtmpdump to get episodes from Nick.com. A full episode on aforementioned site is split into several parts (usually 3-5). I dump each of them using rtmpdump (with filenames like "1.flv","2.flv","3.flv","4.flv"), then use mkvmerge to stitch them together into a full episode (e.g. "full episode.mkv").

Usually, the resulting file plays fine, but for some episodes, there is an issue where stitched file has glitchy image for one or two of the fragments used in stitching (see picture below). Playing this particular fragment on its own (source flv file) works fine.



Here is what I tried to resolve the issue on my own:

1. redownloading the fragments - doesn't help
2. using ffmpeg and flvjoin instead of mkvmerge - doesn't help, still having the same issue
3. unpacking flv files with flvextractor, then joining .264 streams into mkv file, joining .aac streams into mka file, then muxing them together - doesn't help

The only working way I found is to reencode flv files, then stitch them (or do it simultaneously in something like VideoPad)

Can anyone please help me figure out how to stitch these files without reencoding them?

Here are the files I'm having this issue with: https://drive.google.com/folderview?...00&usp=sharing

Thank you in advance!