Creating MPEG artifacts on purpose

[iker]

Hi there, I know it sounds odd, but does anyone know how to create or introduce MPEG artifacts in a video on purpose. It's an effect i'm looking for, for a project i'm doing, and i'd like to have them inserted in certain parts of the picture. Just like a "trail" of "macroblocks" when an mpeg is corrupted, or something similar... I don't want them randomly inserted, but insert them on purpose in certain parts as an effect... So corrupting the mpeg manually won't do... Any clues? I use Adobe Premiere and After Effects btw... Thanks!

Ike.

[jimmalenko]

Isolate a section and re-encode it with a lower bitrate - much, much lower than it needs. This should have macroblocks and pixelations all over the place. You'd then just have this clip as a play item on your DVD or whatever you're creating.

[otpw1]

Finally something I'm a MASTER at! But jimmalenko beat me to the topic.
I do have one possible suggestion however. Use BBmpeg for a couple of seconds longer than you need at an excessively low bit rate & you'll get more artifacts than you can stand.

[iker]

Mmmm... sounds interesting. I could actually reencode the whole video on a veeery low bitrate, then have it as another layer on my editor, and mask the parts I want to affect/effect... shouldn't I? Sounds great!! mmmm but... in that case I would be getting big nasty macroblocks that actually correspond to the blocks in the picture. When a file is corrupt, what you usually get are blocks (B and P blocks) that have to be decoded without their original I block... know what I mean? Jeeezz... it's quite difficult to explain. Let's see, if a hand comes in the picture, and just there you have an error, the decoder has no blocks to refer to, so what you get is a dirty area of "invented" blocks... get it? Would I get that with a very low bitrate...?

Well, whatever.... your advice is good enough for now I guess. I'll give it a try, and experiment with it. Your tips got my mind working! Thanks a lot!!

Ike.

[guns1inger]

In after effects add two versions of the clip to the timeline. Mask one with a mosaic effect and screw around with the speed of the second clip to simulate the B / P frame effect.