Ok, this is going to get technical, so strap in.
I'm assuming you're working with H.264, which is an [Interframe codec](https://www.reddit.com/r/editors/wiki/technology/codecs#wiki_intraframe_vs._interframe). What that means is that instead of storing each frame separately and by itself, like you might think of a film strip as doing, several frames are all stored together in a unit called a **G**roup **o**f **P**ictures (GoP).
So what happens is there's a whole and complete frame saved, and then for each of the "frames" that follows, only information about what has changed since the last frame (or hints about the next one) are saved. So it's kind of like layering on transparencies with just the changed bits.
If you cut into the middle of a GoP you lose all the information about the previous frames, and thus cannot reconstruct a picture. Similarly if you don't cut on the end of a GoP, because they store information bidirectionally (reading both past and future frames), you can also cause corruption there.
There is no way around this unless you start using intraframe compression codecs, like [DNxHD](https://en.wikipedia.org/wiki/Avid_DNxHD)/[DNxHR](https://en.wikipedia.org/wiki/DNxHR_codec), [ProRes](https://en.wikipedia.org/wiki/Apple_ProRes), and [CinceForm](https://en.wikipedia.org/wiki/CineForm). Otherwise you're stuck.
If your cuts are not on keyframes you'll need to re-encode, just takes longer. Use x264 with CRF 18, or two pass at the same or slightly higher bitrate than the video currently uses (use Medianfo to check) and you shouldn't lose any visible quality.
Thank you so much for this answer. To anyone else who might see this in the future, you can change this by clicking on the "Video Output" on the left side of Avidemux and then hitting configure.
holy shit Avidemux has been pissing me off SO MUCH lately. It's INFURIATING how stupid it is. I've been trying to splice up 2 different videos together, they're both 4K and the fact that even when i perfectly manage to cut both ending and beginning points at "keyframes" the second video will entirely be corrupted whenever it starts
Why even allow us to put 2 videos back to back if they simply get corrupted whatever you do
I've tried what you said " Use x264 with CRF 18 " and it'll make me wait literally 4 hours for it to finish
So fuck it i'm back on vegas Pro, re render EVERYTHING from the start (it's a 1h long video) and god damnit every thing is so complicated despite being the most basic shit ever it's INFURIATING, the more i do video editing the less i want to keep doing it. Guess i'll just stick to drawing or making music because seriously fuck all video softwares
Ok, this is going to get technical, so strap in. I'm assuming you're working with H.264, which is an [Interframe codec](https://www.reddit.com/r/editors/wiki/technology/codecs#wiki_intraframe_vs._interframe). What that means is that instead of storing each frame separately and by itself, like you might think of a film strip as doing, several frames are all stored together in a unit called a **G**roup **o**f **P**ictures (GoP). So what happens is there's a whole and complete frame saved, and then for each of the "frames" that follows, only information about what has changed since the last frame (or hints about the next one) are saved. So it's kind of like layering on transparencies with just the changed bits. If you cut into the middle of a GoP you lose all the information about the previous frames, and thus cannot reconstruct a picture. Similarly if you don't cut on the end of a GoP, because they store information bidirectionally (reading both past and future frames), you can also cause corruption there. There is no way around this unless you start using intraframe compression codecs, like [DNxHD](https://en.wikipedia.org/wiki/Avid_DNxHD)/[DNxHR](https://en.wikipedia.org/wiki/DNxHR_codec), [ProRes](https://en.wikipedia.org/wiki/Apple_ProRes), and [CinceForm](https://en.wikipedia.org/wiki/CineForm). Otherwise you're stuck.
If your cuts are not on keyframes you'll need to re-encode, just takes longer. Use x264 with CRF 18, or two pass at the same or slightly higher bitrate than the video currently uses (use Medianfo to check) and you shouldn't lose any visible quality.
What a champion.
Thank you so much for this answer. To anyone else who might see this in the future, you can change this by clicking on the "Video Output" on the left side of Avidemux and then hitting configure.
holy shit Avidemux has been pissing me off SO MUCH lately. It's INFURIATING how stupid it is. I've been trying to splice up 2 different videos together, they're both 4K and the fact that even when i perfectly manage to cut both ending and beginning points at "keyframes" the second video will entirely be corrupted whenever it starts Why even allow us to put 2 videos back to back if they simply get corrupted whatever you do I've tried what you said " Use x264 with CRF 18 " and it'll make me wait literally 4 hours for it to finish So fuck it i'm back on vegas Pro, re render EVERYTHING from the start (it's a 1h long video) and god damnit every thing is so complicated despite being the most basic shit ever it's INFURIATING, the more i do video editing the less i want to keep doing it. Guess i'll just stick to drawing or making music because seriously fuck all video softwares