Muxing and Demuxing affect quality?

[KiLLa]

Hi, im a total newb so pls dont yell if this sounds completely stupid. As far as i know muxing and demuxing refers to joining and cutting of video right? Ok well if this is the case then does muxing and demuxing (or joinning and cutting) have any affect on the video quality. I suspect no, but i just want to be sure that repeated cutting and joining wont affect my video. Thanks

[FOO]

Muxing and demuxing refers to mixing audio and video into one
stream (file ) or taking them apart. Cutting and joining is (obviously)
cutting streams (audio + video) into smaller pieces or gluing them
together.

Theoretically these operations cannot affect quality, but in
practice they sometimes cause problems like audio & video
being out of sync.

[KetchSumAir]

If you're gonna repeatedly cut mpeg files, you should try to do it at I-frame boundaries. You do have a hit when cutting mpeg files that aren't cut on a I frame boundary because it has to construct one (all mpeg streams have to start with I frames).

Unless you're really doing some hacking, it'll be un-noticable, but cut after cut, in the same GOP structure is similar to making a 'copy of a copy' on a copy machine.

I don't believe avi-type files have this problem, but I don't know 4sure.

[VidGuy]

It's a little worse than that - not only does it need to be an IFrame - but the GOP needs to be closed - if any of the P or B frames after the cut refer to a frame that is earlier than the cut, you'll have a problem.

That's why it's usually better to use closed GOPs if you're going to be editing an MPeg file.

[KiLLa]

Thanks alot guys, i think i get the idea now. KetchSumAir especially with your "copy of a copy" analogy helpd me get the picture.

[poopyhead]

your "copy of a copy" analogy

maybe if you cut/join

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demux and muxing by themselves shouldn't have any effect