Video Hex Editing Possibilities

[Veditor]

Hey everyone,

I'll give my question first, then context after.
My question: Is it possible to change an MP4 video file's "cover art" / "thumbnail" (the image you see that represents a video in the file explorer) IN the hex code, or in a hex editor?

I'm a video editor and there are times I want to change the "cover image" or "thumbnail" of a video, but the only way to change it that I've found is to own a MAC as they have a quick and easy means of drag and drop to change it 
So I started looking into hex editing and saw that an "ftyp" atom exists, which was described in the video as essentially the header info for a video file (please correct me if I'm wrong I've only watched some 3 videos on the topic).

Which makes me curious if I can just change a couple values in the hex code. The image itself will always be a screenshot or still image FROM the video, so can't I just change where it choses the screenshot/still image in the video?

Example: I have a video that's 15 seconds long, the video thumbnail in file explorer shows what the frame at 5 seconds in is, but I want it to be the frame at 10 seconds in. Is this a possible thing to do?

If so I would greatly appreciate any assistance in the matter as this is a field I'm ignorant of. I'm good at researching, but lack the experience you all have.

[thephil]

I know too little about the MP4 format to answer your actual question (can it be done with a hex editor) but I do remember that FFmpeg can add thumbnails:

https://stackoverflow.com/questions/54717175/how-do-i-add-a-custom-thumbnail-to-a-mp4-file-using-ffmpeg

Maybe that's enough to get what you need?

[tv84]

What the heck this has to do with test gear?

[modoran]

There is no need to own a MAC to edit a video file. You can do it in windows or linux without problems. ffmpeg and multiple programs based on it can do it.

[Veditor]

I saw a post about hex in this category, but after I posted realized there might have been a better place to post LOL so it doesn't have anything to do with testing. Just an ignorant user trying to find help in his endeavor. Apologies

[Veditor]

Ooooh I had not come across that in my researching I will look into it thank you!

[Veditor]

Correct yes you dont need to own a MAC, what I was referring to was the ease that they have for this singular matter.
Literally involves opening up properties to the video, and dragging and dropping the image you want to use. That's it.

No third party software, no crazy skills. 5 seconds of effort haha. That's all I meant by that remark.

But I'm going to look into the ffmpeg, if you by chance know of any other safe programs please, I would greatly appreciate them. I've tried different file and video browsing software like XnView, but have come up short. And this one software I found "tageditor" I think it's called. Had way too many comments saying it had a virus so never bothered looking further into that one

[radiolistener]

On linux you can use ghex program as a hex editor for files.

[pcprogrammer]

Not sure if Avidemux can do this just like you want, but it is available on both windows and linux.

I tried dropping an image into a stream, but it complained about the dimensions being different. So it looks like it could do it as long as the image has the same dimensions as the video width and height wise.

[Aldo22]

ffmpeg is made for this kind of things.
https://www.bannerbear.com/blog/how-to-set-a-custom-thumbnail-for-a-video-file-using-ffmpeg/